Depends on who your performance chart data vendor is. I would most certianly use MCT at the loss of one of my engines on takeoff, depending on the takeoff weight. If the jet is maxedout at 830k, you are gonna need every bit, just get busy putting it up. If it is at 450k, maybe not so much... Second segment climb data is predicated on MCT on the remaining engines. Besides, you need every ounce of thrust to get the jet sped up and cleaned up as quickly as possible. If you leave the thrust reduced, you are off the charts and now a test pilot, let us know how it comes out. For me, I don't want to be on the 6 O'clock news that bad.

Reduced thrust (also called FLEX) takeoffs are only to save maintenance money. For you, USMCFLYR, think of as intentionally turing most every takeoff into a critical field length takeoff, depending on the thrust reduction taken. If you end up rejecting the takeoff at V1, minus a few knots, you had better be on your game that day, you are about to use up a bunch of brakes and tires. I can't count the number of heavy takeoffs that I have done where when the PNF said V1 and I looked at the runway remaining thinking, there is no way we would be able to stop. So far, have not had to test it. Thank God

 

USMC:

The reduced-thrust concept was new to me, too, upon training for my first airline job. I was told:

The last 10% of an engine's rated-thrust is where 90% of the engine failures occur.

As a guy with an engineering background, I can buy that, from a fatigue, manufacturing tolerance, or materials variance perspective.

Thrust is not linear with RPM; it is exponential. 90% rpm is roughly 50-60% of total thrust available at 100% rpm. Small reductions in rpm are big reductions in thrust, and the probability of engine failure is directly proportional to the amount of thrust coming out of the tailpipe. One instructor told me a 2% rpm reduction lowers the probability of failure by 50%.

The numbers must bear it out...I don't think the FAA would approve it otherwise.

Given the same background as you, I was surprised to find that heavy-weight takeoffs in the 747 (sim) were easier at reduced thrust than lightweight, with any power setting. Why?

The sim instructor almost always fails an outboard engine, giving you the maximum assymetric moment-arm. Higher weights mean faster rotation and V1/V2 speeds.

And the faster you are going, the more effective the vertical fin and rudder. Reduced thrust lowers the assymetry.

 

Thanks to everyone for your explanations of the Reduced Takeoff Thrust (FLEX). Phlyer - I threw that around the ready room and got the same reaction out of the military only trained pilots, but the reservists explained it in somewhat the same manner as you.

USMCFLYR

 

I haven't read all of the previous posts, so if this is a repeat, I apologize.

Engines failures are very rare nowadays but something like over 95 % of engine failures occur during max power takeoffs. When we did TRT takeoffs on the C-141, it always felt like the plane was gonna rattle to pieces!

 

Having worked in PE at NWA for a couple years I can agree with pretty much everything being said. Using De-rates/flex/optimized or whatever you want to call it, you can almost double the time between overhaul while reducing your chance at an engine failure. In fact the TBOs have gotten so high that the fan blades start to deteriorate and we need to come up with fan blade deterioration mode to go along with the drates on both the 57s and 320s.

Even on the 9osaur we can do overspeed which is by admission a poor mans de-rate.

 

on the 777ER we always use reduced power takeoffs. i think most airlines use it. we have a boeing laptop that we put in all the numbers and it is checked by my co-pilot and myself. we get the number of paxs and load form a load master and it works out great. but I can see if you dont check all the numbers it can get you in a bind fast.

 

On a turbine engine, you would expect most failures to occur at higher power settings. As stated, there is a very large percentage power increase in the last few percentage points of RPM.

A piston engine is different though. The typical mechanical failure (other than those due to loss of oil) occurs when REDUCING power after a high power run. The crankshaft, rods, and other parts "unwind", which encourages any weak components to fail. This why it's a good idea not reduce power in an piston ASEL until you have enough altitude to glide to a good landing site.

 

First, great discussion.

Second, someone mentioned that second segment is based, always, on max toga power. Not on the 744 or the 777 as far as I understand. On the 744 the charts (we still use charts) tell you if you are climb/runway/obstacle restricted and your max weight is restricted by, well the most restrictive restriction (sorry it's late). On the 777 the OPT tells you the same without pointing it out (as is noticible on the charts). So, if you are 395 ton or 295 ton it doesn't matter. Don't get me wrong, if I lost an engine I'd hit the toga buttons again. I tried it in the 777 sim as the instructor wanted us to do it the hard way, no toga button, and it climbed like a pig. I imagine an airplane with tired engines would be worse. So, stupid yes, but I think not actually incorrect.

 

Not related to your tailstrike but myself and my co-pilot had to D/H from Dubai to Osaka, Japan earlier this month in first class on one of your 777. You guys run a class act...............