Flex and Derate

Question 1

What are the five limitations to formaly consider when we limit thrust on take offs?

Answer 1

1. Field Length Limit
2. Climb limit
3. Tyre speed limit
4. Obstacle limit
5. A regulatory maximum thrust reduction

Question 2

What’s the regulatory max thrust reduction under EASA for jets and props?

Answer 2

40% for jets
25% for turboprops

Question 3

What about MRJT1?

Answer 3

Limits Flex take-off reduction to a max of 25%

Question 4

What’s Tflex max?

Answer 4

Temperature that defines the regulatory max thrust reduction

Question 5

What’s derated thrust according to AMC 25-13?

Answer 5

a take-off thrust less than the maximum take-off thrust, for which exists in the AFM a set of separate and independent, or clearly distinguishable, take-off limitations and performance data that complies with all the take-off requirements of CS-25. When operating with a derated take-off thrust, the value of the thrust setting parameter, which establishes thurst for take-off, is presented in the AFM and is considered a normal take-off operating limit

Question 6

What is the primary advantage of Derated thrust take-offs compared to FLEX take-offs?

Answer 6

Lower rated thrust will lead to lower values of Vmcg and Vmca and this can, in some circumstances, avoid a Vmcg limited take-off, paradoxically leading to a greater MTOM at a lower thrust setting

Question 7

What’s the implication from the mandatory availability of a full set of performance data?

Answer 7

• A derated thrust take-off is considered to be a normal take-off and therefore can be carried out both on dry runways and on wet and contaminated runways, subject to the AFM data and other operating restrictions
• Because the take-off speeds are calculated at the lower thrust the derated thrust setting is considered to be a limit, and therefore full thrust or TOGA thrust cannot be selected, even in an emergency, until the harzard area for Vmcg and Vmca is well passed. Airbus do not allow TOGA to be selected until the aircraft has achieved the minimum flap retraction speed

Question 7

What’s the implication from the mandatory availability of a full set of performance data?

Answer 7

• A derated thrust take-off is considered to be a normal take-off and therefore can be carried out both on dry runways and on wet and contaminated runways, subject to the AFM data and other operating restrictions
• Because the take-off speeds are calculated at the lower thrust the derated thrust setting is considered to be a limit, and therefore full thrust or TOGA thrust cannot be selected, even in an emergency, until the harzard area for Vmcg and Vmca is well passed. Airbus do not allow TOGA to be selected until the aircraft has achieved the minimum flap retraction speed