every airplane is different

8/10/2019 Every Airplane is Different

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Every airplane is different. Unlike learning to drive a car, you can't just hop from oneplane to another. A pilot needs familiarization (and in some cases, a whole new type oflicense) to fly a different kind of plane. Some are piston-powered; some are jet-powered. Some have electrically-driven controls; some are hydraulically-driven. Somehave emergency oxygen; some don't. And so on. All the switches, dials, and knobs in the

cockpit control the various aircraft systems, and every aircraft has different systems.

Let's take a very popular airliner, the 737. And of course, different 737s are different, solet's just invent a 737 that we can use. A typical one. Here's a photo of a 737.

Pretty typical small-body airliner. For our example, we're going to be flying a 737-600, amodernized 737 with glass-cockpit displays and digital avionics.

So, before we can talk about what all the switches in the cockpit do, we need to knowwhat systemsthe 737-600 has onboard. So without further ado, here is a non-completelist of all the systems that the pilot or copilot might need to manage:

Engine:Our 737 has two CFM56-7 turbofan engines with thrust-reversing capability.

The engines are started by an APU (auxiliary power unit) -- the APU is itself a mini-jetengine that is used to start the two big boys under the wing. (The APU is started by thebattery, if you're curious.) Fuel flow to the engines is electronically controlled.

Fuel:The 737 has three fuel tanks: one in each wing, and a center tank in thefuselage. Electrically-powered fuel pumps transfer fuel from the tanks to theengines. Each tank has two redundant fuel pumps, for a total of six. The center tankdrains first, then the wing tanks. Normally the left center fuel pump sends fuel to the leftengine, and vice versa, but there is a cross feed valve that opens to allow the left centerpump to provide fuel pressure to the right engine in the event the right center pump fails(or vice versa).

Hydraulics:The engines power three redundant hydraulic systems (systems A and B,and the standby system) which actuate the flight controls (elevators, rudder, ailerons)


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that maneuver the aircraft in flight. The hydraulic system also powers the landing gear,flaps, and slats, thrust reversers, as well as a few other minor things. System A and Beach power a subset of the preceding list, with the standby system providing emergencyhydraulic power to the critical systems only.

Electrical: Each engine (including the APU) has its own generator that can power theaircraft's electronics (lights, avionics, galley, in-flight entertainment, etc.). When theengines are off, the aircraft uses an onboard battery to power its systems. There is also astandby battery in the event the main battery is drained. The aircraft can also acceptexternal ground power from a mobile generator. Each electrical source (battery,generator, ground power) can be hooked up to one of two transfer buses that move theelectricity to aircraft systems. Typically in flight each engine generator is hooked up toone of the transfer buses. In the event one electrical source (APU, battery) must powerboth transfer buses, a bus tie system connects the two buses.

Bleed air: Bleed air (siphoned from each engine) powers the air conditioners and anti-ice system, and pressurizes the hydraulic and fuel pumps. The airplane is split into two

separate "zones" which can have their own temperature settings. The aircraft can alsoaccept external air from a mobile air cart.

Oxygen: The 737 has two independent oxygen systems -- one for flight crew and one forpassengers. In the event of depressurization, the oxygen masks will drop and oxygencanisters will supply pressurized oxygen to the passengers and flight crew.

Navigation:The 737 is equipped with two independent GPS antennas and three IRUs(inertial reference units). An IRU is a gyroscope that records changes inacceleration. By integrating these changes over time, the airplane can track its position,though it gets increasingly inaccurate over time.

Radios: The 737 has three communication (COMM) radios and three navigation (NAV)radios. The COMM radios let the pilot talk to ATC and the NAV radios let the pilotnavigate to or from ground radio navigation stations. There's also an onboard weatherradar that sends out radio waves ahead of the plane looking for storm clouds.

OK, let's get started. I'll start with the pilot's side of the main panel.


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back-course. When these modes are active, the pilot gets additional help in guiding theplane down to the runway. The HP/IN button to the right of that button toggles betweenAmerican and European units. The RST button on the bottom left resets the instrumentto displaying straight and level, in case it "tumbles" during heavy maneuvering. (Youshould only press this button when the plane actually isstraight and level.)

Below the standby flight display is the standby HSI (horizontal situation indicator -- it'sa heading indicator that also has the ability to navigate you to a waypoint). The knob onthe standby PFD sets the altimeter setting (again, more on that later). The two dialsbelow the standby HSI set the course that the pilot would like to fly to or from one of tworadio navigation fixes he would have tuned in (e.g., I wish to fly to the Oakland VOR onthe 090 course). The dials show the course you dialed in with the knobs, and indicatehow accurately you are flying that course.

Above the standby attitude indicator is a small dial labeled YAW DAMPENER. The yawdampener helps the pilot smooth out turns by coordinating aileron and rudderinput. When the bar is centered, the turn is smooth. When the bar slides left or right,

the yaw dampener needs to add right or left rudder to the turn to smooth it out. This letsthe pilot check if the yaw dampener is working properly.

There is one little light above the PFD; this is a warning light that tells the pilot whenthat the below-glidesope alert is active. (The glideslope is the proper glide path down toa runway. If you're too far below it, you're going to get leaves in your engines.) Pressingthe light inhibits the warning, in case the pilot really does know what he's doing.

To the right of that light, above and between the PFD and ND, are two knobs; thesecontrol what systems are linked to the pilot's displays. Normally the left screen showsthe PFD and the right screen shows the ND, but if one of your screens fails, you could

switch up which screen displays which system. These knobs let you do that.

To the right of those knobs are a set of three lights in a well; these light up to tell the pilotwhen the autopilot has disconnected, the auto throttle has disconnected, or there is anerror on the FMC (again, FMC explained later). The switch to the right tests thelights. The switch to the right of thatswitch is the master warning lights switch; itcontrols the brightness of all warning lights, and tests all warning lights.

Below the well are three more lights. They light up to tell the pilot when the speed brakeis extended, when the speed brake should notbe extended, and when the autopilot isfailing to trim the aircraft properly (an aircraft is in trim when it can fly straight and levelwithout continuous input from the pilot or autopilot; an aircraft out of trim will slowlypitch up or down).

To the left of the pilot's PFD is a digital clock with count up timer and sweep secondhand. The CHR button on the top left of the clock face starts/stops/resets thechronometer. The two buttons on the top right are used to set the time and togglebetween local time/UTC time/date display. On the bottom-left, the two buttons controlthe elapsed time counter, which is used to time the entire flight. Lastly, on the bottom-right, the + and - buttons are used to set the time.

Below that is a switch that toggles between the normal (hydraulic system A) or alternate(hydraulic system B) nose wheel steering (NWS) system. (NWS turns the nose wheel on

the ground and allows the plane to steer during taxi.)


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Alright, next up, the knobs below the pilot's PFD and ND. On the very left is a pull-leverlabeled FOOT AIR, to make the pilot's feet comfortable, followed by WINDSHIELD AIR,which defogs the main windows.

To the right are five knobs. They control the brightness of the four displays (PFD, ND,

upper DU, and lower DU) and the brightness of the panel itself (flood lights that light thewhole panel).

Then to the right we've got two more knobs, that control the brightness of thebackground lights, and another set of flood lights that light the top portion of the panel(which we'll see later).

Now to the right of those knobs we see a small screen with a keyboard. That's the FMC,or flight management computer. This is a computer into which the pilot enters the routehe wants to fly, the altitude he wants to fly it at, and all sorts of other information aboutthe flight. From that the computer calculates the best speed to fly each leg of the flight,how long it will take, whether there's enough fuel, etc. The pilot can also enter in

restrictions (can't be above 250 knots below 10,000 feet, for example), and the autopilotwill obey those restrictions. The FMC has a multitude of other functions, like findingnearby airports in an emergency, or calculating holding patterns, etc. There's pages andpages of features.

To the right of the FMC is the lower DU, and then the copilot's very own FMC. There'ssome stuff above his FMC that we can't really see well, so let's take a closer look to theright of the previous image.

The big round handle is the landing gear lever. Pull it up and the gear retracts; push itdown and the gear extends. Above the lever are three landing gear lights. They're greenwhen the gear is down, red when the gear is in motion or not fully extended, and unlitwhen the gear is up. It's typically a good idea to check for "three green" before landing.

To the left of the gear lights is the flaps indicator. The flaps are a pair of flat surfaces on

each wing that can extend outward to increase the surface area of the wing. This allowsthe plane to fly at slower speeds (say, for landing). Right now the needle shows the flaps


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at 0 (fully retracted). They can be extended all the way out to 40 for very slowlandings.

To the left of the flaps indicator are the auto brake controls. The auto brake canautomatically start braking after landing. The top light illuminates when the auto brake

disarms due to a malfunction, reminding the pilot that it's now his job to stop theplane. The middle knob sets the braking intensity, from OFF (no auto braking) up to 3(hard braking), with a special RTO setting (rejected takeoff -- hold on to your handrests).

The two lights below the flaps indicator light when the flaps are moving or extended,respectively. The light below the auto brake knob illuminates when there is amalfunction in the anti-skid system, warning the pilot not to apply excessive brakepressure and cause a skid.

To the left of all that are a pair of small knobs, a switch, and two pushbuttons. The rightknob controls where the aircraft gets its calculated reference airspeeds -- important

airspeeds that must be called out during takeoff. They can be automatically calculated bythe FMC, or as a fallback, entered manually using this knob. The left knob controls whatmax. N1 limit is displayed on the upper DU. Like the reference airspeeds, it can beautomatically calculated by the FMC or manually entered. The setting appears as a redline on the N1 dials displayed below on the DU.

The FUEL FLOW switch below the N1 setting knob controls the fuel flow indicator;normally it shows the fuel flow rate, but can temporarily act as a fuel "triptometer" --showing fuel used since the last reset, and marking a reset point.

The three buttons to the right of that switch control what's shown on the lower DU,

either engine information (ENG) or information on the aircraft's other systems(SYS). The C/R button is cancel/recall -- press it once to "cancel" any warnings shownon the DU (makes them disappear), and press it again to "recall" those warnings (makesthem reappear).

To the right of the landing gear lever are the copilot's PFD and ND, the copilot's cockpitillumination controls, and air controls (not shown). They mostly mirror the pilot's.

OK, let's move on to mode control panel (MCP). It sits on top of the main panel:


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On the left side are the controls for the pilot's ND. The top-left knob (MINS) is wherethe pilot dials in the minimum approach altitude. This is the lowest the pilot can gobefore he mustsee the runway to land. If he can't see the runway, he has to abort thelanding. Setting this knob will let the plane say "MINIMUMS" when the pilot reachesthis altitude, as a reminder. Then, going right, we've got an FPV button that togglesdisplay of the flight path vector on the PFD (basically a little circle showing you whereyour airplane is trending; e.g., if it floats above the artificial horizon you know your planeis climbing). Then a button (MTRS) that toggles between metric and English units forinternational flights. And lastly a knob (BARO) for changing the altimeter setting: that'sthe outside surface air pressure. The pilot needs to do this so the altimeter indicates anaccurate altitude.

Second row: The first switch (VOR1/ADF1) toggles the left data block on the ND betweenVOR and ADF information. (VOR and ADF are two kinds of radio navigation.) Thenwe've got a knob that sets which of the different screens the ND is displaying (currentlythe MAP screen). The ND can show an overhead map view (as shown), or a plan view, oran approach and landing view, etc. The next knob over sets the range of the ND (thezoom knob). And then there's another switch that's like the VOR/ADF switch on the leftside, but for the right data block. (These data blocks are not currently shown ND.)

The bottom row of buttons toggle on and off the display of different "data layers" on theND. In the photo the ND is pretty sparse -- it's just showing the compass rose and courseline. The pilot could use these buttons to show weather radar, nearby airports,topographic terrain, etc.

To the right of that cluster, spanning the remaining width of the MCP, are the autopilotcontrols. When the pilot is not actually flying the airplane by grabbing the yoke, he isdialing in instructions to the autopilot using this panel.

At the very left side of the MCP is the course knob and window. This knob sets aninbound or outbound course to fly towards a radio navigation facility (e.g., fly to the

Newark VOR via the 270 radial). Below and to the right of that knob is the F/D (flightdirector) switch. Turning on the flight director is like "assisted autopilot": The autopilot


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doesn't actually fly the plane, but shows you on the PFD what you should be doing to flythe plane in the way it wants you to. It's extra guidance for the pilot who still wishes tohand-fly.

Just above the F/D switch is a tiny little light labeled "MA" (for master -- though it's unlit

so you couldn't tell). There are actually two of these lights; one on the left side and oneon the right -- you can see the right one on the other side of the photo. These correspondto the two FCCs (flight control computers) that power the autopilot. If the left light is on,the left FCC is doing the F/D calculations. If the right is on, the right FCC is doing theF/D calculations. Normally the left FCC manages the pilot's F/D, but if the pilot's FCCfails, it could be managed by the copilot's FCC.

Moving over to the right, we've got the A/T (auto throttle) arm switch. The auto throttlecan control the throttles automatically to maintain a set airspeed or N1. To the right ofthe switch is a knob that dials in the airspeed/N1 setting, and above it a display showingthe current airspeed/N1 setting. There are lines moving out to the bottom-left andbottom-right, connected to buttons. These enable the different auto throttle modes -- N1

(maintain an N1), SPEED (maintain an airspeed), and LVL CHG (level change; setsthrottles appropriately for climbs and descents).

There's also a small button to the left of the knob called C/O (changeover), which togglesthe display between airspeed (in knots) and Mach number. At higher altitudes, speed inMach becomes more important than speed in knots.

The other small button to the right of the knob is the SPD INTV (speed intervention)switch. If your FMC is calculating your speed for you, but you temporarily want tomaintain a different speed, press this button and dial in your speed. Press it again toreturn to flying the FMC's calculated speed.

Above that button is the VNAV button, which turns on the vertical navigation autopilotmode. This mode will fly the vertical profile programmed into the FMC, beginningclimbs and descents as the FMC commands.

To the right of the VNAV button is the heading knob and related buttons and window.This knob is used to set a heading for the autopilot to fly. The button just below the knobturns on heading mode, commanding the autopilot to fly that heading.

To the right of the knob is a row of three buttons. The top turns on LNAV (lateralnavigation) mode. This mode flies the plane through the waypoints programmed intothe FMC. Turning on both LNAV and VNAV mode will have the plane fly exactly the 3Droute programmed into the FMC. The middle button turns on VORLOC mode, wherethe plane flies to a VOR (radio navigation fix) using the onboard nav radio and thecourse dialed into the course window. The bottom button is APP (approach) mode,where the plane flies an ILS signal down to a runway. ILS is a very accurate radionavigation system that can guide a plane precisely onto a runway for landing.

Next column to the right is the altitude setting. We got a knob and a window for settingthe altitude, and two mode buttons: ALT HLD (altitude hold), and V/S, which holds aspecified vertical speed. To the right of the knob is a small ALT INTV (altitudeintervention) button that works like the SPD INTV button. Then we got a knob and awindow for dialing in a desired vertical speed in feet per minute.

Moving right is a grid of four buttons. These control the two autopilot computers (A and


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B). The top row of buttons turn on autopilot command mode (where it has totalcommand over the aircraft), and the bottom row turns on CWS (command with steering)mode. CWS is a special mode where the pilot pushes the controls to get the plane flyingin the way he wants, and then releases the controls -- the autopilot then takes over theflying. There are two redundant autopilot systems, and both must be active to make an

autopilot-controlled approach and landing.

The big bar below the grid of buttons disengages the autopilot and gives the pilot fullcontrol of the aircraft. To the right of that grid are some duplicated controls from the leftside that are in easier reach of the copilot.

The other panel we can see in this image is the Ground Proximity Warning System(GPWS). The panel is below the copilot's ND, containing three large black switches.

The GPWS warns the pilot when it detects that the aircraft may hit the ground. Thethree switches are used to turn on and off three types of ground-proximity audiowarnings: "TOO LOW - FLAPS" (when the plane thinks you may have forgotten to

extend your flaps before landing), "TOO LOW - GEAR"(when the plane thinks you mayhave forgotten to lower your gear before landing), and "TOO LOW - TERRAIN" (whenthe plane thinks you may have forgotten about that mountain between you and therunway).

Above and to the left of the switches is a warning light indicating when the GPWS isinoperative, and a SYS TEST button that tests the GPWS.

Now let's look above the main panel, on the glare shield:

The red Fire Warning light is bad news when it lights up, but you can silence the alarmbell by pressing it. The yellow Master Caution light is also bad news; pressing it"acknowledges" the caution and turns off the light. To the right of the Master Cautionlight is a grid of lights that indicate what is generally wrong with the airplane. (Nothingis illuminated right now, but examples are FLT CONT [flight controls] and ELEC

[electrical system].) The copilot has his own Fire Warning and Master Caution lights, aswell as a separate grid of different annunciators.


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The CLOCK button on the very left operates the chronograph, same as the CHR buttonon the clock face.

Let's take a look at what's to the left of the pilot's seat:

The wheel on the right side of the image is the tiller wheel, used to steer the airplane onthe ground. Below it are two knobs; the forward one controls the brightness of the maplight (the red-capped light on the left side of the image). The rear knob has no function.

Behind the knobs is the pilot's emergency oxygen mask.

Let's move on to the throttle console now!

At the center are the throttles. Push forward to burn more gas, pull back to savemoney. There's one for each engine. There are also paddles behind each throttle lever


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that control the thrust reversers. Pull up to apply reverse thrust during landing. Thereare buttons underneath each throttle grip (not shown) that engage TO/GA (takeoff/go-around) mode. Press either button and the throttles automatically set for either a takeoffor an aborted landing. The black buttons on the side of each throttle grip cause the autothrottle to disengage, giving throttle control back to the pilot.

The pair of levers below the throttle are the fuel cutoff levers. Pulling either of theselevers down will cut off fuel to that engine. They're used to shut the engines down in anemergency or as part of a routine shutdown.

The big wheel is the trim wheel. If the plane is floating up hands-off, push the wheelforward to apply forward trim. And vice versa. Nurse the wheel as needed to get theplane to fly straight without any pressure on the yoke from the pilot. To the right of thetrim wheel is the trim indicator.

Next to the trim wheel is the parking brake lever, and behind it a light that illuminateswhen the parking brake is set. Also next to the trim wheel is the speed brake lever -- pull

back to deploy the spoilers and slow down; push forward to clean up the plane and speedup.

To the right of the throttles is the flap lever, which sets the flap position.

Below the flap lever are the stabilizer trim cutout switches. There's one switch for theautopilot's automatic control of trim, and another switch for the pilot-controlled electrictrim system. If either system were malfunctioning and trimming the aircraft incorrectly,you could disable it and just trim the plane manually using the big trim wheel. Note thatthese are backuptrim cutout switches -- the normal trim cutout switch is on the yoke.

OK, let's move away from the throttle quadrant to the bottom portion of the centerconsole. At the top are the bright red fire extinguisher handles, labeled "1" and "2" (forengine 1 [left] and 2 [right]), and "APU" for the APU fire extinguisher. To the left of theengine 1 extinguisher is the OVERHEAT switch, which selects between redundant A and

B engine overheat detection circuits. Below that is a light that illuminates if an overheatis detected in the left engine, and below that a switch that tests the A and B detection


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circuits.

Between the engine 1 and APU handles are lights that warn of: a fire in the wheel well, afault in the A or B fire detection circuit (depending on the position of the OVERHEATswitch), a fault in the APU fire detection circuit, or a discharged APU bottle (you only get

one!).

Between the APU and engine 2 fire extinguisher handles is a similar set of test switchesand warning lights for the right engine, and a big black BELL CUTOUT button(obscured) that silences the fire warning bell if the pilot should get sick of it. To the rightof the engine 2 handle is the bottle test switch and lights that tell the pilot that each ofthe three extinguisher bottles is working properly. There are also a pair of lightsindicating that the left or right bottles have already been used.

Moving down to the very top-left side of the center console is the COMM1 radiopanel. The left window shows the active frequency: the frequency the pilot would betalking over if he were to key in the mic while COMM1 was set. Then to the right we have

the standby window, which is where the pilot dials in the next frequency he wants to talkto. When he's ready to switch frequencies, he presses the transfer button in between thetwo windows, and he's on a new frequency. The two knobs set the larger and smallerdigits of the standby frequency. There's also a test button and an on/off button belowthe right and left windows, respectively. The grid of six buttons in the bottom centerchoose which radio the COMM1 panel is connected to: There are three VHF radios, twoHF radios, and an AM radio. The HF SENS knob is used to set the sensitivity whenCOMM1 is connected to the HF radio: HF is a very long-range radio system used inoverwater flights, and can require fine-tuning of sensitivity.

Moving right, we have the cargo file panel. We have two green lights that light up when

the TEST button below it is held down, to show that the two cargo fire extinguisherbottles are working. We got two small knobs that choose between each of two firedetection circuits for the forward and aft cargo locations (so two circuits per location,two locations total). To the right is a light that illuminates if a fault is detected in any firedetection circuit. Below the knobs are two lights that illuminate should a fire be detectedin the forward or aft cargo compartment. To the right of those lights is a guarded button;flip the guard and press down to extinguish the cargo fire. It doubles as a light tellingyou you've already discharged your bottle.

To the right of that is the COMM2 radio, which works the same as the COMM1 radio.

Below the COMM1 radio control is the NAV1 radio control. This works like the COMMradios except the pilot doesn't talk over the radio; the airplane uses the radio signal tonavigate to a station. There's a test button that drives the NAV1 needle (on the ND or thebackup HSI) to a known heading; if the needle is on that heading, the radio is working.

To the right of NAV1 are the weather radar controls. The left knob sets the gain(sensitivity) of the weather radar, and the right knob is used to tilt the radar up or down,to scan for storm clouds above or below. The buttons select different display modes,such as WX (weather only) or WX+T (weather and turbulence). In case you're curious,the radar can detect turbulence by noticing when rain droplets change direction as theyfall.

Then, moving right, we've got the NAV2 radio, same as the NAV1 radio.


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Below the NAV1 radio is the audio selector panel. The top row of buttons sets who thepilot is talking to when he keys in the mic. He can talk over COMM1 or COMM2, he cantalk to the flight attendants or to all the passengers, etc.

The two rows of knobs below that set the volume for each of the many different radios

and other audio sources that go into the pilot's headset.

The bottom right switch is a backup push-to-talk switch for mic keying. (The normal PTTswitch is on the yoke.) Move up to talk over the radio, and move down to talk over theintercom.

To the right is the MASK/BOOM switch, which toggles between the oxygen maskmicrophone and the boom microphone for transmissions. The pilot would only use theMASK position of the oxygen mask deployed in an emergency.

The V-B-R knob controls what audio is filtered out from nav radio stations. In "V", onlyweather information is heard (which is sometimes broadcast over a nav radio). In "B",

both weather information and the morse code identifier is heard. In "R", only the morsecode identifier is heard (to verify that the pilot tuned in the correct station, and thestation is working properly).

The ALT-NORM switch on the right toggles between normal and emergency mode forthe communications system.

To the right of the pilot's intercom controls is the HGS (heading guidance system)controls. The pilot uses this panel to input information into the HGS. The HGS thendisplays telemetry to the pilot over the HUD (more on that later) to help him land. Thepilot presses a button on the left (such as RWY for runway length), then enters the data

using the numeric keypad on the right. Once he's entered all the data, the HGS can thenhelp guide him down to a landing. There's also a clear button and brightness controlsalong the bottom.

To the right is the copilot's mic and intercom controls, which are the same as the pilot's.

Below the pilot's intercom controls is the ADF panel, which controls the ADF, a very oldform of radio navigation. The bottom-left knob switches between ADF mode (fornavigating to the radio signal) and ANT mode (for listening to the radio signal). Theright knob mutes and un-mutes the radio signal. The pilot would listen to the radiosignal to hear the morse code and make sure he's tuned the correct frequency, and ergonavigating to the correct station.

To the right of the ADF radio is the transponder controls. The transponder is a devicethat intercepts an incoming radar beam (from an ATC radar) and sends it back out withinformation about the aircraft. ATC uses this information to get more information aboutan aircraft than it could from just an unmodified radar return.

The top left knob selects between one of two redundant transponders. The middlewindow is the transponder code. Every aircraft is assigned a four-digit code when it'sunder ATC control; you dial it in with the two knobs below and on either side of thewindow.

The top right knob turns on the transponder and sets its mode. XPNDR turns onaltitude reporting, which sends back the plane's current altitude (which can be hard for


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radar alone to determine) with the radar beam. TA additionally transmits the plane'sunique identifier. And TA/RA will also allow the transponder to receive databroadcastfromATC to all nearby aircraft over the radar beam. This data includes thelocations of other aircraft that the radar is picking up.

Note that the four-digit squawk code is different from the unique ID transmitted in TAmode -- the four digit squawk code can be reused many times in a day, whereas theunique Mode S ID is assigned once to one aircraft for all time.

The bottom left knob sets whether to use the pilot's or copilot's altimeter when reportingaltitude back. The middle IDENT button performs an identification function. Thiscauses the aircraft to "light up" on ATC's radar. ATC will often ask an aircraft to "ident"to figure out who they're talking to. The top middle light indicates a transponder failure.

To the right of the transponder controls, below the copilot's intercom panel, is theCOMM3 radio panel, same as the COMM1 and COMM2 panels.

The bottom left panel controls the brightness of the center panel and flood lights.

At bottom center are additional trim controls. The aileron trim controls are on thebottom left, allowing the pilot to trim left-wing-down or right-wing-down if the plane isdrifting left or right. The indicator is in on the yoke. The knob on the bottom right isrudder trim, and its indicator is above the knob

To the right of that is the stabilizer trim override switch. In the NORM position, the yoketrim cutout switch is operational. In the OVRD position, the two trim cutout switches onthe throttle quadrant (discussed above) are operational.

At the very bottom right are the cockpit door controls. The door can be unlocked, locked,or automatically controlled using the right knob. The two lights indicate when the dooris unlocked and when the locking mechanism has failed.

We're almost done -- let's do the overhead console! Let's start with the top half.


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The red switch at top-left controls the in-flight WiFi; it can be in normal or override-offmode.

Below that switch are the IRU controls. At the top we have a window that displays

information, and a knob that controls what information is displayed. It can display thecurrent lat/lon, the wind direction and speed, the airplane heading and speed, etc. All ofthis information comes from the IRS (inertial reference system).

Below that is a knob that toggles the display between using the left or right IRS (there aretwo after all). To the right is a keypad used to enter in the initial lat/lon of theaircraft. (Remember that the IRUs only measure changesin position, so without aninitial position, they can't give any useful information.) Normally this is done using theFMC, but it's here too as a backup.

Below the IRS panel are some warning lights showing when an IRU has failed, or is onbattery backup power, and a pair of knobs that set the left and right IRU mode. IRUs

have to spin up and align before they can be used for navigation, a process that takes 10minutes. So the IRU must first be put into ALIGN mode for 10 minutes or so before itcan be moved into NAV mode. If the pilot is in a hurry, he can put the IRU into theemergency ATT (attitude-only) mode, but he will get no position information and onlyattitude information.

To the left are two slanted sets of lights: That's the leading-edge flaps indicator. Theflaps actually have two components: The part that extends backwards and the part thatextends forwards (the slats). These lights indicate whether the slats are in motion,extended, or retracted.

Below the slats indicators is a single, lone caution light. It illuminates when the PSEU(proximity switch electronic unit) has failed. The PSEU monitors the sensors thatdetermine if the landing gear is up or down, if the aircraft is flying or on the ground, etc.

To the right of the IRS panel is the SERVICE INTERPHONE switch, which turns on abackup system for talking with the flight attendants. Below that is the DOME WHITEswitch, that turns on and off the bright white dome light that floods the wholecockpit. (Not good for night vision.)

Then, one column to the right at the top, is an intercom panel for the observer (a thirdflight deck member who sits in an observer seat).

Below the observer intercom panel are two thrust reverser caution lights that illuminateif there is a problem with the left or right thrust reverser. Below that are two switchesand lights that toggle between the primary and alternate EEC (electronic enginecomputer). Each engine has two EECs, one for backup. The EEC controls the flow offuel into the engine to get a desired power, as set by the throttle, but will also limit poweras necessary to prevent damaging the engine.

Below the EEC controls is the emergency oxygen indicator. The flight crew has its ownindependent emergency oxygen system, and this dial shows how much oxygen is left inthat system.

To the right of that is a switch and a light -- flip the switch to make the passenger oxygenvalves fall down from the ceiling. The light illuminates to show that the passenger


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oxygen is on and flowing to the masks.

Below that are three backup gear-down lights; in case the main ones go out, the pilot canstill be sure his gear is down before he lands.

On the very right is the flight recorder switch, used to test the flight recorder (thatrecords telemetry to the black box in case of a crash). The light to the right of itilluminates if the flight recorder fails. The two buttons to the right of the light test theairspeed warning system that sounds an alarm when the plane busts its maximumairspeed.

Then below that we've got two stall warning test buttons. Press them to test each of thetwo redundant stall warning systems. (A stall occurs when the aircraft is no longer flyingfast enough to generate lift. It's bad enough to warrant an aural warning.)

On to the lower portion of the overhead panel:

At the top-left corner are the flight control systems. The two black switches at the topturn on and off the A and B hydraulic flight control systems, which allow the pilot tosteer the jet in the air. The warning lights to the right of and below those switches warnthe pilot if there isn't enough hydraulic pressure to power the flight controls. There is

also a STBY RUD position on each switch that switches rudder control to the standbyhydraulic system.

The bright red switch in the middle of that panel turns on the alternate flaps system,which uses the standby hydraulic system to get the flaps down or up in anemergency. The red switch turns on the system, and then the smaller switch to the rightraises or lowers the flaps.

Below and to the left are another pair of black switches; these turn on and off hydraulic Aand B power to the speed brakes. The lights to the right warn of speed brakefailures. Below that is the yaw dampener on/off switch and failure light.

Moving right, we have a lone switch that turns on and off the cockpit video camera, and


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then below it a digital display; this shows information about the electrical system (ampsand volts being put out by the battery and generators). Below that are three warninglights indicating when the battery is powering things that the generator ought to bepowering, or other electrical failures. To the right is the MAINT button, which is used byground personnel to test the system.

Below the warning lights are the controls for the electrical system display. It's split intotwo sides -- the left is for DC equipment, and the right is for AC equipment.

On the right is a knob that sets which electrical system's information is appearing on thedisplay; it can display information from the main battery, standby battery, battery bus,and each of three generator transfer busses, as well as a test mode.

Below that knob is the battery on/off switch -- this is the first switch you'd want to flipwhen you entered the cockpit.

Moving to the right half of the panel (the "AC" half), we've got another knob for setting

which system's information is shown on the panel (standby battery, external groundpower, engine 1/2 generator, APU generator, battery inverter, or test mode), and two on-off switches for two electrical accessory systems. Below it is a GALLEY switch thatsupplies electrical power to the galley for "cooking" airline food.

Moving right, we've got two knobs controlling the brightness of the circuit breaker lights(which are behind the copilot's seat) and the overhead panel lights.

Right again, and we get seven switches in two rows and a plethora of lights. These arethe heating/anti-ice controls. The top row of switches controls the window heat(defog/anti-ice). There are four heated windows (four switches), and the center switch

tests the overheat detection system. The lights illuminate when the heating system is onor when it's overheated and automatically turned off.

Below that are the probe heat switches. The pitot probe sticks out from the outside ofthe airplane and measures ram air pressure; this is used to calculate airspeed. It must beheated to avoid icing. The switches turn on probe heat, and the lights illuminate whenthere is a problem with the probe heaters, or when the auxiliary probe heaters areactivated.

The next panel down contains the anti-ice switches. On the left we have the wing anti-iceswitch, and two lights showing that the anti-ice valves are open. On the right, we havethe engine anti-ice switches, one for each engine, and lights showing when each valve isopen. The additional lights indicate problems with the engine anti-ice system.

Moving right, at the top, are the temperature controls. The top middle knob setswhether the temperature dial below is showing the passenger cabin air temperature orsupply duct air temperature. To the left and right are dials indicating how much coldoutside air is being mixed with hot engine air to produce the desired air temperature foreach of the two passenger cabin zones. At the bottom are two knobs that control thetemperatures of each of the two zones. There is an auto setting and a manual cold/hotsetting. The warning lights indicate an overheat condition when there is not enough coldair to bring the hot air down to the desired temperature.

Moving back to the left side, in the middle, are the navigation sourceswitches. Normally, the pilot's radio navigation instruments are powered by the NAV1


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radio, and the copilot's by the NAV2 radio, but this switch lets you set one radio to powerboth sets of instruments.

The IRS switch does the same thing, but for the two IRSes, and the FMC switch for thepilot and copilot FMCs. The displays source knob and displays control panel switch

control whether each DU control panel and source switch (discussed earlier) configuresits own DU, or whether the panels both configure the same DU.

To the right of that is the standby battery controls. The two red switches connect anddisconnect the standby batteries from DC (left) or AC (right) power. The center switchturns on and off the standby battery. The middle warning light illuminates when thestandby battery is off. The left and right lights illuminate when the standby battery ispowering the DC or AC busses.

Moving right to the center column, there is an EQUIP COOLING panel, with twoswitches and two lights. The switches control the equipment cooling fans (supply andexhaust), which must be on to keep the avionics cool. The lights indicate when the fans

are off.

Below that are the emergency exit lights controls. The switch turns on and off theemergency exit lights, and the light indicates when the exit lights are illuminated.

Moving right, we get a big cluster of lights above and below four switches. These are thehydraulic pump switches. There are four hydraulic pumps: an electrically-powered andan engine-powered pump for each engine. The inboard switches power the electricpumps, and the outboard switches power the engine-driven pumps. The top warninglights indicate when a pump detects low hydraulic fluid pressure or an overheat of anelectric pump.

One of the bottom cluster of lights will illuminate if any one of the many exit doors areopen in the aircraft. All of these lights should be off before the plane starts taxiing.

Moving right, we see a dial above a set of switches. These are the air systemcontrols. The dial indicates the air pressure in the air ducts. The switch above and to theright of it turns on and off the recirculating fan, which recirculates air (and interestingodors) throughout the cabin. Below that is the overheat test button that tests theoverheat detectors.

The switches below and to the left and right of the dial control the left and right packs. Apack is an air conditioning unit that provides conditioned air to the cabin and otheraccessories -- it can be turned off, placed in auto mode, and forced to maximum output(HIGH). Directly below the dial is the isolation valve switch, which controls the isolationvalve. When the valve is closed, each pack has its own independent source of air. Whenthe valve is open, the packs can share air between them.

The button below that switch resets a tripped overheat light. The lights to the left andright of the button indicate when a pack has overheated.

Below those lights are three switches; they control the source of air. The outboardswitches select bleed air from the left and right engine; the middle switch selects bleedair from the APU.

Above the air control panel are three lights; they light up to show cautions related to the


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air system, such as a "dual bleed" situation (air being fed from both engines and the APUat the same time).

Moving back to the left side, below the navigation controls, is a dial surrounded bylights. The dial indicates the temperature of fuel in the tanks (to watch out for freezing

fuel). The blue lights to the left and right illuminate if a fuel valve is closed. The bluelight below and to the center illuminates if the cross feed valve is open. The orange lightsflanking that light illuminate if either of the two fuel filters is being bypassed.

Below that are the fuel pump controls. The big knob in the top center opens or closes thecross feed valve. Below that are controls for the two center tank fuel pumps, and low-pressure warning lights. Below those switches are controls and warnings lights for thetwo fuel pumps for each of the wing tanks.

To the right, we have a single switch, the ground power switch, which toggles on and offexternal ground power (if it's hooked up to the plane). Below that are the generatorcontrols. The big black switch in the middle turns on or off the automatic bus transfer

system, that automatically transfers power between buses to ensure AC power isavailable. The lights to the left and right indicate if the engine 1 or engine 2 transferbuses have failed.

Below that is a row of four switches. The outboard switches control the left and rightengine generators, and the inboard switches control the two APU generators. The lightsilluminate when a generator is not powering systems because another generator is doingthe job for it.

Below that is a row of four caution lights, indicating faults in the generator system. Thenbelow that we've got an EGT dial for the APU. (Since the APU is itself a mini-jet engine,

its EGT must also be monitored.) To the right is the pilot's windshield wiper knob --park, intermittent, low- and high-speed; the copilot's wiper controls are just to the right

Moving to the center column, we've got the No Smoking and Fasten Seatbelts switches(though No Smoking has been taped over with a new meaning -- "chime"), and twobuttons. The left makes a "bing-bong" chime that gets a flight attendant at your beckand call, and the right sounds a horn to external ground personnel working near yourjet. The light below the GRD CALL switch indicates when a flight attendant or groundperson would like to talk to you (the reverse of the call buttons).

Moving right again, below the cluster of lights, is the cockpit voice recorder (CVR)controls. The black grille in the middle is the cabin mic for the voice recorder. The redbutton erases the CVR's memory banks (this can only be done when on the ground,before you get clever). The green button tests the CVR and illuminates the little light tothe right if everything is working.

Below that is the cabin pressure dial. The dial has two needles, one indicating thecurrent cabin altitude (the altitude that the cabin "feels" like it's at given the airpressure), and one indicating the difference between the outside and inside airpressure. (It can't be too high.)

To the right of that is the ALT HORN CUTOUT button, that silences the landing gearwarning horn, if, for example, the pilot knows the landing gear is down but for whatever

reason the airplane still thinks the gear is up, and is complaining loudly about it.


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The dial below the cabin pressure dial is the rate of change of cabin pressure -- itindicates ear-popping "descents" or "climbs" in cabin pressure.

Moving over to the right, we see the cabin pressure controls. We have two windows andtwo knobs, for setting the cruising altitude (the cruising cabin pressure will be based on

this) and the altitude of the airport we're landing at (so that by the time we land, thecabin pressure has been equalized). To the right of those windows is a dial indicating theposition of the outflow valve, which releases excess pressure to the ambient atmosphere.

Below that are the manual outflow valve controls. The top switch opens or closes thevalve when in manual control, and the knob below toggles between automatic, alternateautomatic, and full manual control of the outflow valve.

Moving to the left side of the very bottom row, we have a row of four wideswitches. These turn on and off the landing lights, which illuminate the runway atnight. Then we have a pair of smaller switches -- these are the runway turnoff lights,which illuminate the left or right side of the aircraft. The switch to the right of that turns

on the taxi lights, which are less blindingly bright than the landing lights.

Moving right again, we have the APU start switch, which is used to power the APU. Oncethe APU is powered up, you can start the engines. Which brings us to

The engine start panel is to the right of the APU start switch. There are two knobs, thatcontrol the engine starters for the left and right engines. The starter has four modes:GRD (ground start), OFF, CONT (continuously monitor the engine and automaticallyrestart if it dies), and FLT (in-flight restart). The switch in the middle determines whichigniters to use -- only the left or right engine, or both engines.

Moving right again are a set of five more lights switches. They control, in order, the logolights (lights up the airline logo), position and strobe lights (to help other planes find usat night), anti-collision lights (same purpose), wing lights (to mark the edges of ourwingtips at night), and wheel well lights (to light up the wheel well for maintenancecrews).

At the very bottom left is the HUD (heads-up display), currently folded up. You can pullit down to get helpful symbology superimposed over the view ahead. The knob controlsHUD brightness.

Below the overhead panel is the standby compass and a switch controlling the compasslight:


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There are some controls sprouting out from the yoke too:

As you can see, the pilot has a handy checklist in the center of the yoke with a movabletab to keep his place. On the left side, the two trim switches trim the airplane nose-upand nose-down. The button on the side disengages the autopilot. On the right side, thenumeric display can be set so the pilot doesn't forget his flight number. Not shown is thepush-to-talk switch, which is held down when the pilot wishes to speak over the radio.

And lastly, behind the copilot's seat is a large bank of circuit breakers:


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And that's it! I hope you enjoyed this tour!

every airplane is different

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