Indications of engine overboost on B737 EFIS
 

Hello Gents,

I'm looking for clarification of the indications of engine overboost on the B737-400. The indications to my knowledge are that a red light illuminates on the N1 gauge if overboost occurs and remains illuminated for as long as the condition exists. It will therefore extinguish once the overboost condition ceases. The LED will indicate the N1 reading and do not brighten in intensity.

Only EGT indication brightens during engine start up if a temperature exceedance is likely due to rapid rise in temperature approaching 725 deg C; the LEDs on the EGT increase in intensity during this situation.

The brightening in intensity of LEDs on N1 does not happen in any condition but does occur for a Hot start on the EGT gauge; it is therefore not an indication of overboost.

Any assistance or details on these points would be really appreciated. Also, if anyone has knowledge of overboost indication on the 757 I'd be interested to know more. However, it is really the 737 that I'd like to resolve.

Thanks

If I recall correctly the red light on the N1 indicator will come on if N1 is above 106%, nothing else.

The only indication of overboost you have is that actual N1 is more than TO/GA N1, read: you will have to check that yourself.

I must admit it has been quite some time I flew the classic

Thanks for the feedback - I thought the red light on the N1 gauge indicated an exceedance.

From my (old) 737 manual regarding the red light above the N1 gauge:-

Not sure what an 'overboost' is................:confused: Where is that Manifold Pressure gauge..............?

Both N1, N2 and EGT gauges have the same indication for exceedance of MAX ie Limit RPM and EGT.. Operation as described above.

I'm with you

being in a pedantic mood

I would have called "out-of Limits"

unless you felt a kick in the pants like an afterburner kicking in

From the QRH
 

Engine Overboost

A significant thrust overboost capability exists which could be useful in emergency situations. This overboost capability should only be considered when ground contact is imminent. In an emergency situation ‘firewalling the thrust levers' should be considered. Overboosting the engines when the situation is not sufficiently serious unnecessarily shortens engine life and increases the potential for engine failure. This condition could result in an EGT or N1 exceedance. LAND AT NEAREST SUITABLE AIRPORT.