Is it possible that derated thrust takeoffs are safer than normal takeoffs?

Manfred
  • Is it possible that derated thrust takeoffs are safer than normal takeoffs? Manfred

    The reason for my arguments here are (assuming that you have sufficient runway distance):

    That with less thrust, less force should also be required to hold the aircraft as desired, and possibly the aircraft should be easier to control and fly when the engine fails than if it does so with the thrust set to full blast.

    An engine event, such as a bird strike, might (?) be less likely to have catastrophic consequences for e.g. the turbine blades when they are not running at full thrust and their design limits.

    Never having actually commanded an aircraft, are any of these ideas correct?

  • The reasons presented at ground school for the benefits of de-rated thrust takeoffs were twofold:

    • less chance of catastrophic engine failure during takeoff
    • less overall wear between overhauls

    It is from this standpoint that reduced thrust takeoffs are safer.

    As you point out, these are only authorized when the weights, temperature and runway length allow, but for the EMB-145 virtually every takeoff we did was eligible for reduced thrust.

    You point about ease of control with an engine out is countered by engine out procedures which involve setting max thrust on the remaining engine (for two-engine ops). During takeoff roll in the EMB-145XR, this puts the other engine at 117% power. With the exception of flying near $V_{MC}$ (for light twins) the extra thrust is a benefit and not a hindrance to control and if this is at or after $V_1$ you'll want the thrust to go flying.

    Your question about a bird strike is going to go one of two ways:

    1. the bird hits the N1 fan and goes through the bypass ducting
    2. the bird hits the N1 fan and is ingested into the N2 compressor stages

    In either scenario a reduced thrust vs full thrust takeoff is not going to make a huge difference, but scenario 2 will be far more destructive to the engine than scenario 1.

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