Back in the old days, the seventies and eighties, it was up to us pilots to push the engine to its limits and to make sure its limits were not exceeded. After every flight where the engine held together, we thought we had done it again. But after engine failure after engine failure it became obvious we were either exceeding the limits and not telling any one, pushing the limits repeatedly was causing cumulative damage, or both.
Understanding the liquid nature of metals will help you prolong the life of your very expensive engines. Most of which follows comes from my Air Force Boeing 707 manual. I will agree that engines these days are made better, last longer, fail less often, and have lots of computers to keep you out of trouble. I also concede that the chart above and the technical details below may not remotely reflect the engines strapped to your airplane. But all of this is an excellent primer on possible failure modes for your jet engine.
Our Boeing 707 squadron went through a few years where we lost an engine a month. With four aircraft, each with four engines, the odds were not good. Here's what we learned from all that: just because you are operating the engine within its published limits doesn't mean you are taking good care of it.
Everything here is from the references shown below, with a few comments in an alternate color.
Figure: Expected Engine Life, from 1C-135(E)C-1, Figure 7-3A.
In the early eighties, the Air Force started adding "Engine Creep" paragraphs to flight manuals. These paragraphs remain the best thing I've ever seen on the subject, despite a few flaws in logic.
[Technical Order 1C-135(E)C-1, pg. 7-4]
|EGT - °C||RPM (N2)||CREEP|
|450||95%||1 unit per hour|
|525||97%||5 units per hour|
|555||100%||50 units per hour|
|585||101%||2500 units per hour|
Every airplane I've flown since the B-707 automatically records these "excursions" over the limits and the later ones even make note of the time and date. But now, things have gone to the next level:
Figure: EEC Location, from FSI G450 PTM, pg. 7-22.
In the Gulfstream GV/G450/G550 world, FADEC is either "Full Authority Digital Engine Control" or "Full Authority Digital Electronic Control." Either way, the thing running the engine is not the pilot, it's this:
The EEC, the Electronic Engine Control is the part of the FADEC that interprets your power lever movements as requests and turns those into fuel and guide vane commands that gives you more or less power, but it will not allow you to damage the engine.
But what if you do? On this particular airplane, the airplane sends off an e-mail to Gulfstream, the airplane's director of maintenance and chief pilot. It will rat me out to me.
FSI G450 PTM, FlightSafety Interaction Gulfstream G450 Pilot Training Manual, Volume 2, Aircraft Systems, October 2008
Technical Order 1C-135(E)C-1, EC-135C Flight Manual, USAF Series, 15 February 1966.
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