TMAX is the standard temp envelope, you can extend into TMAXFLEX with an increased temp envelope. You can assume a temp hotter than TMAX, but you cant operate if the actual temp is hotter than Tmax.T max is max OAT for given conditions. It is possible to have the reduced thrust setting, indicated with T flex, higher than this.

Setting T flex = 65°C, you are saying to the aircraft:Hey, now please give me just as much thrust as you would be able to provide if it were this hot outside: 65°C. The maximum setting is determined by the 25 per cent requirement, hence it is not possible to set Tflex=85 because it would represent a larger thrust reduction than is allowed.

A1) The max flex setting is read from RTOW charts or obtained from PC performance calculation.

However, if it really was 65 degrees outside, you may not take-off. it is too hot. Maximum OAT for takeoff is usually lower than that. Tmax(OAT) <> Tmax(flex). The highest values for flex setting are pseudo-temperatures and only serve to set an appropriate level of engine thrust, real OAT for take off is limited by Tmax(OAT).

A2) T(flex) must be less than Tmax(flex) but once this condition is satisfied, T(flex) may be actually more than Tmax(OAT). Takeoff with OAT higher than Tmax(OAT) is prohibited.Tflex cannot be higher by more than 25% of OAT. Basically, the requirements for a flexible take off are :

1. Tflex is > OAT2. Tflex is > Tref3. Tflex is < or = Tmaxflex

For A320 only : Tref = ISA+30, Tmax = ISA+40, Tflex = ISA+55 (Tref and Tflex will vary accordingly for A319 and A321).

Simple example : airfield elevation 3000 ft.

--> 2 deg C per 1000 ft lapse rate = 3 x 2 = 6 degrees C--> 15 degrees standard temp at sea level = 15 - 6 = 9 degrees C

--> Tflex from above = 55 + 9 = 64 degrees C, this means that your flex temp for take off should not exceed 64 degrees (25% of rated thrust or Tref). This is the last row of flexible temp you will see on your RTOW chart corresponding to that particular ATOW.

Tmax for the above example would be = 3 x 2 = 6 degress C

--> 40 + 6 = 46 degrees ( at 46 degrees OAT you cannot take off )

NOTE:The use of FLX TEMP adds some “safety” margins for T/O.Indeed if V1 = 160 kt with FLX 65 →V1 TAS = 172 kt.If the OAT = 35 °C that day, the effective V1 TAS = 164 kt.The STOP calculations are computed on V1 TAS 172 kt (as well as would be the GO calculation on the FLX V2 TAS).This somehow corresponds to a V1 gain of 8 kt, which could equate to 8 (FLX TEMP - OAT) meters gain on distances.The RTOW charts are not exactly the same for A320 and for A319/A321 (Octopus).They also may have different presentations according to airline’s choice: entry with GW or with TEMP. For Octopuscharts, the influence factor corrections are provided either in 2 lines or 4 lines.For A320 charts, the corrections are found in FCOM 2-02-24. In all cases the principle to determine the T/O data is thesame:1. Determine the MTOW and apply the influence factor corrections.For Octopus charts, as per the order, those factors are provided on the chart:- for the 1st influence, apply the correction from first 2 lines (unless OAT TVMC in which case the last 2 linesapply) - NO SPEED CHECK VERSUS V1 / VR / V2 MIN, VMU is necessary,- for the 2nd or 3rd influences, apply the corrections as follows:- if only 2 lines are provided, achieve a SPEED CHECK,- if the SPEED CHECK is NOT SUCCESSFUL, T/O is NOT POSSIBLE UNDER THE PRESENTCONDITIONS,- if 4 lines are provided, USE THE 2 BOTTOM LINES (no speed check required).

2. Determine the FLEX TEMP and apply the influence factor corrections.For Octopus charts:- for the 1st influence correction, apply the FLX and Speed corrections as required, and CHECK SPEEDSVERSUS V1 / VR / V2 and VMU,- for the next one, same method. If 4 line corrections are provided, you may use the BOTTOM 2 LINES with NOSPEED CHECK; this is very conservative.If the SPEED CHECK is NOT SUCCESSFUL, FLX is NOT POSSIBLE. Use MAX T/O and the SPEED associated toMTOW or the SPEEDS ASSOCIATED to CURRENT GW if all those speeds are lower.NOTE:For Octopus charts, if GW is lower than any GW provided on the charts, apply all influence corrections first. Then applythe speed decrement corresponding to lower GW, e.g. 1 kt/t, and check the resulting speed versus V1, VR, V2 min andVMU.T/O CONFIGURATION CHOICECONF 1 + F / CONF 2 / CONF 3 may be elected for T/O.A high T/O CONF is preferable to minimize tailstrike risks, or on rough runways to decrease the T/O speeds.A low T/O CONF (1+F) is preferable to optimize the climb gradient more specifically in hot weather.As a consequence the general criteria to determine the best T/O CONF are:- HIGHEST FLX TEMP (engine life saving),- LOWER T/O SPEED and- PREFERRED CONF FOR COMFORTABLE A/C HANDLING (e.g. tailstrike).The preferred T/O CONF is thus CONF2 as long as it does not induce a reduction of FLX TEMP higher than 5°.CONF 2 provides the best compromise to fulfil these criteria.Various other factors influencing Take-off