The aim of this presentation is to provide you with some background and visual information, as a complement of the recent release of FCOM and QRH OEB-45 and AFM TR A320-286, A330-293 and A340-294, about the blockage of AOA probes on aircraft equipped with conic AOA cover plates.
This presentation starts with some words about the reason that led Airbus to launch a new design of AOA cover plates. You will then be provided with some details about the in-service event, which occured on an Airbus aircraft equipped with conic AOA cover plates, and led Airbus to issue the subject temporary procedures. Finally the presentation provides some details about the procedure for the A330/A340 and for the A320 Family aircraft, especially the visual effects in the cockpit to enter in the OEB procedures.
• The conic AOA cover plates aim at protecting the AOA root from the ice crystals phenomenon.
• Installation of conic cover plates started in February 2012:• 170 A330/A340 aircraft• 520 A320 family aircraft
• One equipped aircraft had an in-service event
December 2012Flight Operations Webconf
Presenter
Presentation Notes
Originally, Airbus decided to launch a new design of the AOA cover plates, in order to prevent ice accretion on the AOA root due to ice crystals phenomenon, which may occur at high altitude. Two types of conic cover plates have been designed for the two probe types. The installation of the conic cover plates started in February 2012, and at the time of the in-service event, about 170 A330/A340 aircraft and a bit more than 500 A320 Family aircraft received the new cover plates. One Airbus aircraft equipped with the conic cover plates had an in-service event. No in-service event has been reported on aircraft equipped with flat cover plates over more than 100 millions of flight hours. This explains why Airbus decided to issue temporary procedures only for aircraft equipped with conic AOA cover plates.
• With pitch attitude continuously decreasing, PF reacted by applying permanent (for about 20s) sidestick order in the full backward position. • Pitch angle continued to decrease and AC to descend• A/THR reduced the thrust due to Speed increase (Selected Speed
305kts)• The flight crew elected to switch ADRs to OFF• With reversion to alternate law, the High Angle-of-Attack protection
was no longer available.• Pitch attitude was recovered.• Flight crew diverted and performed an uneventful landing.
• Airbus decided to provide, as a precautionary measure (root cause of the in-service event still under investigation), the operators with temporary procedures for aircraft equipped with conic AOA cover plates.
• Goals:1. Provide cockpit effects to detect two or three AOAs
sending same constant values2. Provide procedure to revert to alternate law
December 2012Flight Operations Webconf
Presenter
Presentation Notes
Along with Flight Operations Transmissions (FOT), temporary procedures have been released for the A320/A330/A340 aircraft equipped with conic AOA cover plates through OEBs and associated AFM Temporary Revisions (TR). This is done as a precautionary measure as the root cause of the in-service event is still under investigation. Two main goals led the development of the temporary procedures: Anticipate a potential Alpha Prot activation due to AOA signals remaining at the same constant value, by providing the flight crew with visual effects in the cockpit to identify an issue with the AOA signals. Provide a simple procedure to prevent an undue activation of the Alpha Prot. Of course, one of the big challenges in this development was to determine conditions to apply the OEB procedure, that cannot occur in ‘normal’ conditions (without issue on the AOA signal). This resulted in relatively ‘heavy’ conditions, but in which each word has an importance. This is detailed in the following slides.
Let’s first have a look to the details of the procedure for A330/A340, and we will then look at the A320 Family procedure to see the similarities and the differences between the two aircraft families.
On the A330/A340 aircraft, one visual effect is the behavior of the Valpha Prot strip (the black and amber strip) under certain conditions. Indeed, when the aircraft is under stabilized flight path conditions (meaning with a vertical load factor equal to 1, like in a climb phase with no modification of the vertical profile and no turn), if the AOA signals remain at a constant value, the Valpha prot strip constantly increases as the Mach number increases (with an increase in speed or more likely with an increase in altitude), until completely and permanently hiding the VLS strip. Such a behavior could be observed without AOA issue, if the load factor increases. This is why it is very important to be under stabilized flight path condition, before considering a potential issue with the AOA signal.
• Procedure entry points - cockpit effects:A LOCK message remaining displayed even with speed increase to VFE CONF1 – 10kt:
December 2012Flight Operations Webconf
FLAP 0 Selection
Presenter
Presentation Notes
The second entry point of the procedure is linked to the behavior of the slats: Under normal conditions (with no issue on the AOA signal), depending on the aircraft weight and the AOA value, the SFCC keep the slats in the extended position (and displays the A LOCK message on the ECAM) as long as a certain speed is not reached. When this speed (which is a function of the aircraft weight) is reached, the SFCC automatically command the slats to retract. With no AOA issue, the retraction of the slats always occur before reaching the VFE of the CONF1 - 10 kt. If the slats remain extended when the aircraft speed reaches VFE CONF1 – 10kt, it is symptomatic of an issue with the AOA signal.
• At anytime, if the aircraft goes to an unmanageable pitch down attitude, even with sidestick in full backward position: reversion to alternate law: 2 ADRs….OFF
December 2012Flight Operations Webconf
IMMEDIATELY
Presenter
Presentation Notes
In addition to the two previous entry points in the OEB procedure, quick procedure actions are provided, if the aircraft goes to an unmanageable pitch down attitude, even if the flight applies a continuous sidestick deflection in the full backward position. In such a situation, it is necessary to immediately revert to the alternate law by switching two ADRs to OFF.
Finally, the core of the A330/A340 aircraft procedure is made of two main ideas: Limiting the Mach number and Reverting to the alternate law. The first idea is achieved by stopping an increase of the aircraft speed and altitude. And this is done in the purpose of preventing the activation of the Apha Prot (which is a function of the Mach number). The second idea aims at preventing an undue activation of the Alpha prot coming from AOA signal at a constant value while the Mach number increases.
For the development of the procedure for the A320 Family aircraft, as much as possible, Airbus tried to keep the procedure similar to the A330/A340 procedure. However, due to differences in the design of the aircraft, some entry points and action steps differ from a procedure to another.
• Procedure entry points - cockpit effects:In stabilized flight path (Nz=1), Alpha Max strip increases and hides completely the Alpha Prot strip:
December 2012Flight Operations Webconf
Increase in Mach
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Presentation Notes
The main difference in design between the A320 Family aircraft and the A330/A340 aircraft is linked to the display of the Valpha Prot strip (black and amber strip) and the Valpha Max (red strip) strip. Indeed, on the A320 Family, per design, when the vertical load factor is equal to 1 (in stabilized flight path conditions), the Valpha Prot strip and the Valpha Max strip remain limited at a value of VLS - 2kt. This means that (with or without an issue in the AOA signals), in stabilized flight path conditions, the Vapha Prot strip and the Valpha Max strip can not hide completely the VLS strip. However, one visual effect on the A320 Family, which occurs when there is an issue with the AOA signals, in stabilized flight path conditions and with an increase in the Mach number, is that the Valpha Max strip increases and hides completely the Valpha Prot strip.
• Procedure entry points - cockpit effects:With AP ON and increase in load factor (Nz>1), Alpha Prot strip moves by more than 30kt
December 2012Flight Operations Webconf
Increase in load factor
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Presentation Notes
The second visual effect that can be observed on the A320 Family is the behavior of the Valpha Prot strip out of stabilized flight path conditions. For example during a turn or a pitch variation that involve an increase in the vertical load factor. In such a situation, the Valpha Prot strip (black and amber) is no longer limited to VLS – 2kt, and it increases. If the vertical load factor returns to a value of 1, for example when the turn is completed or the pitch attitude is stabilized, the Valpha Prot strip decreases again towards VLS – 2kt. What is remarkable is that with the AP ON, thus using the AP gains for turns or pitch variations, the variations of the Valpha prot strip never exceed 30 kt. On the contrary, when the AP is not ON, for example during manual flight, the variations of the Valpha Prot strip can exceed 30 kt. Therefore, with the AP ON, during maneuvers that involve an increase in the load factor, an increase in the Valpha Prot by more than 30 kt is symptomatic of an issue with the AOA signal.
• Procedure entry points - cockpit effects:A LOCK message remaining displayed even with speed increase to VFE CONF1:
December 2012Flight Operations Webconf
FLAP 0 Selection
Presenter
Presentation Notes
Finally, similarly to the A330/A340 aircraft, slats remaining in the extended position along with an acceleration of the aircraft may be a symptom of an issue with the AOA signal. The entry point is therefore very similar than for A330/A340, except for the value of the aircraft speed for which an issue with the AOA signal can be detected. Indeed, it can be observed, on heavy aircraft, such as A321 at heavy takeoff weight, that with no issue on the AOA signal, the retraction of the slats only occurs at a speed very close to VFE CONF1. Therefore the 10kt margin in the A330/A340 procedure could not be kept for the A320 Family. For the A320 Family, an issue with the AOA value can be detected when the slats remain in the extended position, and the aircraft speed reaches VFE CONF1 Also, it has to be noticed (as mentioned into the FCOM-OEB procedure) that the Overspeed warning triggers at VFE CONF1 + 4kt. The margin in terms of speed between the detection of the issue with AOA signal and the triggering of the overspeed warning is very small.
• At anytime, if the aircraft goes to an unmanageable pitch down attitude, even with sidestick in full backward position: reversion to alternate law: 2 ADRs….OFF
December 2012Flight Operations Webconf
IMMEDIATELY
Presenter
Presentation Notes
As for the A330/A340 aircraft, in addition to the three previous entry points in the OEB procedure, quick procedure actions are provided, if the aircraft goes to an unmanageable pitch down attitude, even if the flight crew applies a sidestick deflection in the full backward position. In such a situation, it is necessary to immediately revert to the alternate law by switching two ADRs to OFF.
As far as the core of the A320 Family procedure is concerned, the main ideas remain the same as for A330/A340 aircraft: Limiting the Mach number (by stopping the acceleration and climb) and Reverting to the alternate law (by switching two ADRs to OFF).
