Free Flight, Free Speech

Omega wrote:All wise airlines I know of that operate Boeing aircraft, use TOGA during takeoff to prevent engine wear. This is completely normal, common practice.

KL-666 wrote:You are technically right that you may use toga on take off.

Btw. I have never heard a pilot stating he uses it for avoiding wear. If he does it, he does it out of laziness after having worked so hard on the fms. He does not want that work to go to waste.

HJ1an wrote:Save wear on the throttle lever maybe

The advantage of having such a system is the ability to reduce wear and tear on the engines by only using as much power as is actually required to ensure the aircraft reaches a safe take off speed.

Reduced-thrust takeoffs trade some excess capability for reduced engine wear. Operating temperatures, turbine speeds and overall stress levels are lower, and the engine is less likely to fail. This is especially important when you consider that the possibility of engine failure is the basis for all those takeoff performance margins in the first place.

The closely held studies by engine manufacturers are based primarily on fixed derate thrust data because operators typically do not report assumed temperature thrust data. However, equivalent temperature levels using assumed temperature techniques can be favorably compared to the results.

Component wear in the hot section, particularly the high-pressure turbine, can be dramatically improved. One available GE Aviation study of failure modes in the CF6-80 indicated that regular use of the maximum 25 percent fixed derate resulted in a near order-of-magnitude increase in cycles to failure — from 1,000-2,000 cycles to 5,000-10,000 cycles. This study identified thrust derate as the “most important factor in reducing turbine blade failures and deterioration.”

Reducing EGT has been tied directly to improved engine wear and time-on-wing maintenance intervals. EGT deterioration, a major factor in engine removal and overhaul, also has been shown to be retarded by reduced thrust. Related deterioration of fuel flow also is countered by reduced-thrust operations. According to the GE study, each 10 degrees C of EGT deterioration translates to a 1 percent fuel-flow deterioration. Limiting this effect has obvious advantages in maintaining a higher level of specific mileage for a given amount of on-board fuel.

Manufacturers approximate the effects of engine use against the engine’s designed operating life through severity analysis, which considers the total picture of degraded performance, rotating parts life and parts deterioration and failure. Parameters like rotor speeds, internal temperatures and internal pressures are used to gauge the total severity. Analysis has shown that these parameters are directly affected by two factors: stage length and the level of reduced thrust used. The takeoff phase places the most stress on an engine and is thus weighted more heavily; however, other factors emerge during cruise on longer flights.3 Thus, although any carrier will benefit, short-haul airlines that put several cycles a day on their aircraft would gain the most from a reduced-thrust policy.

Considering the extreme operating conditions of a turbine engine’s hot section, limiting wear should be an obvious goal. Turbine blade fatigue, in particular, is directly affected by high centrifugal forces and vibration stresses, and these loads have a direct relationship to increased turbine inlet temperatures. A study performed by the China Civil Aviation Flight College found a 51 percent reduction in blade life after 3,500 hours at 870 degrees C, compared to a 35 percent loss when operating at 705 degrees C, and a near doubling of hot section life overall

KL-666 wrote: I do know that many airlines take these documents the same way i do. And i happily board such airlines

but not the ones who try to spell out the medicine disclaimers only to cover their own arse too.

SHM wrote:

Component wear in the hot section, particularly the high-pressure turbine, can be dramatically improved. One available GE Aviation study of failure modes in the CF6-80 indicated that regular use of the maximum 25 percent fixed derate resulted in a near order-of-magnitude increase in cycles to failure — from 1,000-2,000 cycles to 5,000-10,000 cycles.

This study identified thrust derate as the “most important factor in reducing turbine blade failures and deterioration.”