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# Flight Engineering

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.

Figure: Expected Engine Life, from 1C-135(E)C-1, Figure 7-3A.

### Starting to Understand the Problem

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
• Turbine life is inversely proportional to the number of creep units per hour. The pilot controls the rate of creep by the manner in which he operates the engine. Turbine blades are carefully inspected and measured at engine overhaul. Those which are elongated beyond tolerable limits and those which show evidence of distortion or cracks must be replaced. In extreme cases, the blades may even fail before the engine comes due for overhaul. It can be readily seen from the foregoing creep rate table that when an engine is operated at the lowest temperature and rpm shown, the turbine blades will last 2500 times as long as they will if the engine is operated at the highest temperature and rpm shown. This is the reason that EGT during engine acceleration is time limited. Although the pilot cannot "read" the creep rate of turbine blades, he can "read" the operating temperature of the engine as EGT.
• A definite relationship exists between excessive EGT and premature engine removals. The fuel control normally maintains EGT within a safe margin. However, the control cannot compensate for operational malpractices. Furthermore, under extreme flight conditions or in the event of a malfunction, the regulation of engine internal temperatures can be marginal or even above desired limits. Therefore the pilot must develop a "temperature sense" by thinking in terms of the inter-relationship of the engine control factors. By so doing one can learn either to avoid excessive temperatures altogether or to take immediate action should they occur. Do not use a thrust or power setting higher than is necessary to accomplish the assigned mission.

### Starting to Deal with the Problem

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.

### References

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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