No DERATE Option for Takeoff?

[gfinn12]

I noticed on the takeoff page in the MFD, there is only TOGA and FLEX available. Real world A350's also have a DERATE option. Is this company specific or just not modeled in the ini builds?

 

 

 

IMG_3260.webp

Edited October 27 by gfinn12

[Swisspilot1986]

What's the difference between a derate and a flex?

[Skyrock]

On 11/3/2025 at 9:25 PM, Swisspilot1986 said:

What's the difference between a derate and a flex?

A fixed derate is useful in cases where you need to lower Vmcg (Minimum control speed on ground) and subsequently V1, e.g to increase your performance limited takeoff weight on short and/or contaminated runways. On for example contaminated runways, Flex takeoffs are not allowed, hence you would only be able to do TOGA takeoffs. The main problem in these cases: if you have an engine failure. Now, you have to have a higher VMCG and V1 in order for the rudder to have enough authority to counter the asymmetric thrust during an engine failure with TOGA power. With a fixed derate, in case of engine failure, the remaining thrust on the operative engine remains at the derated thrust level. It's actually prohibited to advance to TOGA with a fixed derate (unless during a windshear or if above F-Speed), because it might lead to a control loss. Therefore, with a fixed derate there is lower asymmetric thrust and with that, the VMCG/V1 can be lower since the rudder can achieve enough authority to counter the moment by the asymmetric thrust at a lower speed. The Performance Limited Takeoff Weight increases in those cases.

Most of the time, your takeoff performance calculator will still present a Flex temp and only in rare occasions (like contaminated runways) it will provide a fixed derate. On Boeing aircraft, a fixed derate and a flex (here called assumed temperature) can be combined (e.g TO-1 42°C), so in case of engine failure by pressing the TOGA button, only the assumed temperature would be removed but the fixed derate would remain. On Airbus aircraft, a fixed derate can not be combined with a Flex, so it's either one or the other. 

Edited 19 hours ago by Skyrock