Hi Guys, a few comments from a maintenance engineers view. Below is an excerpt from the Fault Isolation Manual for the GE CF6-80C. I also work on Rolls Royce RB211-524D4's-G/H2's, CFM's and Pratt & Whitney JT9's. Each manual is pretty much the same when it comes to EGT exceedance. The level of maintenance/inspection is determined by both the actual temperature recorded and the amount of time spent above the yellow/red line. There is a chart that will determine what "Area" the exceedance falls into based on these factors. These areas are normally A, B and C although some engine types have D as well with A being the least critical and C the most critical. For example, an exceedance of just 5 deg for 300 seconds may put you in the same area as an exceedance of 60 deg for 5 seconds! The chart is fairly exponential with each degree rise in temp substantially reducing the time allowed for operation within this area.
Monitor The Egt Trend And Engine Performance. If The Egt Trend Increases Appear Abnormal,Do The Borescope Inspection (amm 72-00-00) At The First Opportunity.
15 Excursions Into Area A Of High Egt Chart Requires The Removal Of The Engine (amm 71-00-02)For Overtemperature Inspection.
A.
IF THE ENGINE IS OPERATED IN AREA A, DO THE STEPS THAT FOLLOW:
1.IF THE CAUSE OF HIGH EGT IS KNOWN, SUCH AS N1 OVERBOOST, MEC RIGGING, EXCESSIVE AIR BLEED, HIGH ELEVATION AIRPORT, TEMPERATURE INVERSION DURING TAKEOFF, OR HOT DAY (OAT AT OR ABOVE FLAT RATING) CONDITIONS, CORRECT THE CAUSE WHERE POSSIBLE.
2.IF THE CAUSE OF HIGH EGT IS NOT KNOWN, MAKE SURE OF OVERTEMPERATURE AND LOOK AT THE
INDICATION SYSTEM. MONITOR THE EGT TREND AND ENGINE PERFORMANCE FOR INDICATION OF TREND INCREASES. BORESCOPE INSPECT THE ENGINE IF INCREASES APPEAR ABNORMAL.
B.15 EXCURSIONS INTO AREA A AND/OR B REQUIRES ENGINE REMOVAL FOR OVERTEMPERATURE INSPECTION.
NOTE:THE ENGINE MUST BE REMOVED FOR OVERTEMPERATURE INSPECTION IF OPERATED IN AREA C.
Like all limits/exceedances, these charts are on the extremely conservative side. The limits and designs of the aircraft/engines take these exceedances into account. For example on the 747-400 and 767 (and i'm sure many other modern jets) once the throttles are advanced to take-off range and the aircraft speed reaches 80 knots (the A/C thinks it's taking off) any EGT exceedance display is inhibited on EICAS for 5 minutes for 'RED' exceedances and for 10 minutes for "yellow" exceedances. The engines are more than capable of continuing the journey to the next port so long as all indications return to within normal range after thrust reduction. At the 'other end' I'll read the highly detailed Tech Log report that you have written - with your accurate recording of temp's reached and times above limit and then perform the required inspections, borescopes and/or change the engine if need be. Oh, yeah - How are you going to do this if EICAS hides the exceedance during Take-off?? Not to worry, EICAS does all this for you giving a nice plot on the maintenance screen of all the temp and time info. You'll know of the exceedance as it will paint the EGT indication box yellow or red for you on upper EICAS - even when the temp has returned to normal. If you really have 'cooked' the engine the turbine blades will give up, become soft due to excess heat, stretch like plasticine, rub against the turbine case and "Bang" you're now dealing with an engine failure as opposed to an exceedance and I'm sure your hand is then forced!
Whilst I would never be so bold as to offer advice on what pilots should or shouldn't do during a flight it would be my opinion that an immediate return would not be required just on the basis of the needle going past the limit line. Just write it up in the Tech Log and/or call your maintenance base for advice. Of course, once I've done your pushback and got your engines going, the moment I unplug my headset and give you a wave - you're in command. If you choose to return for an EGT exceedance that of course is your prerogative - I just wouldn't want to be in your shoes when you're called to The Chief Pilots office for a "Please Explain" We all know the potential costs of an Air Turn Back and I'm guessing you guys have to be able to back-up your "Command' decisions.
This post obviously tilted towards the 747 / 767 so sorry for the long ramble for you pilots who fly other types.
Last edited by Spanner Turner; 1st Sep 2006 at 06:40.
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