Jet Engine Overboosting

[Denti]

Yup, we had the case recently on a 737-300, old style CFM56 (no FADEC) got overboosted during a windshear manoeuver around 20 feet during takeoff, both had to be replaced as per manufacturer instruction for that case. Funny thing is both pilots reportet they saw overheat, however the QAR only showed N2 overspeed.

[gas path]

The Jt9d was a 'part throttle' engine. It would give you what ever you required in the way of thrust, up until the 'speeder spring' in the JFC limited the RPM.
The RB211-22 up to the RB211-524d the fuel control amplifier limited thrust.(N1 and N2)
As 411A states some operators had the EGT channel whilst others, BA for one had it isolated. However if the amp was switched out the only limit came from the FFR, hence the requirement to throttle back before switching the amplifier to override.

The Trent series of Rollers do not detect a TGT exceedance

B777 the EGT EICAS figure turns red for an exceedance and returns to white as the overtemp comes back into limits. However the EGT 'box' remains red until the exceedance page is erased.The exceedance page gives a timeline of temperature and time above.

[wileydog3]

You can overtemp and engine and you can overspeed an engine and both require logbook entries on every jet engine I have throttled. But overboost is a recip term and unfortunately it persists among even many training facilities.
And where this becomes a problem is when some training has the student figure a maximum N1 or Max EPR or whatever before doing a stall series. Rubbish, to use the term. Unless one considers stalls a normal procedure then normal limits do not apply. Firewall or MAX thrust until the thing quits shaking and the stall is broken.
I thought this concept of max EPR on recovery had been invalidated in the 80s with Air Florida 90 going into the Potomac but some still teach stalls in businessjets this way. ?????

[ahramin]

A turbine jet engine always has by its very nature the ability to destroy itself. Whether or not this can be done from the flight deck by bending the power levers over the front depends on what controls the aircraft manufacturer has put in place to prevent this from happening.

Case in point our company had a turbine engine in Africa on a natural gas pipeline (used to "pump" the gas down the pipeline). The pipeline sprung a leak and the engine was sucking in some of this gas so it started to run faster, which pumped more gas out as the leak was just downstream. It just kept going until it (very quickly) self destructed due overspeed.

It doesn't matter what an engine is rated for, if you put more fuel in, it will produce more power, until it breaks.

[Zenj]

In FCTM for B737-200 Boeing has a section for Overboosting

This is what it says !

Engine Overboost 7.18

A significant thrust overboost capability exists which could be used in emergency situations. This overboost capability should only be considered when ground contact is imminent.
Overboosting the engines when the situation is not sufficiently serious unnecessarily shortens engine life and increases the potential for engine failure.
In an emergency situation “firewallingthe thrust levers” should be considered.
This condition could result in an EGT or N1 exceedance.
Land at the nearest suitable airport

[Jonty]

In our company Vol 1 it talks about overboost/overspeed protection. On the RB211 we dont have FADEC but we do have an EEC to stop overboost overspeed. So we can push the thrust levers fully forward and not trash the engine, although we have no EGT protection. Without EECs we have no overboost/overspeed protection and therefore we can trash the engine.

This relates to the RB211E4 on the B757

[exeng]

Rainboe

I remember your incident very well (November 1984). I was on secondment to QF from BA as an F/E and was called from standby to operate a 5th pod flight (SYD - PER) to provide your service with an engine.

We all met up in the Parmelia for a bit of post flight refreshment.

I remember discussing the incident at length with your F/E who was more than a little concerned as to what may be in store upon his return to LHR.


Regards
Exeng

[BelArgUSA]

Sadly, there was a perfectly competent French A320 test pilot that probably would have loved to overboost his engines after a low pass at an airshow, but ended in the trees... but all the electronic junk you have nowadays will not permit to save an airplane and passengers from an accident... If and when I need power, my 53,000 lbs thrust engines will give me 55,000... And I will bend the thrust levers if need be...
xxx
Keep your FADECs for yourselves, Gentlemen, none on my old 747 Classics...
And I love it that way... Ah... the good old days...
Soon at the beach in Brazil, and forget forever all about EGT or N1 limits...
Forever
xxx

Happy contrails