B737-300 Idle N1 question

[Hudson]

During a Battery start (B737-300 simulator) the stabilised idle N1 shows 29.5%. When the generators are placed on-line, the N1 idle drops to the normal approx 22% N1.

Is this normal and if so in what manual are the Battery Start ( No AC power) N1 idle figures to be found?

[DDG]

With nil AC power the MEC goes to flight(high) idle.When AC power is applied the idle power solenoid resets.

Cheers

[TopSwiss 737]

Because of the lack of AC power, the engine control gives you flight idle. I am not sure if it is due to a missing air/ground sensor input or not. Think of it as a kind of fail safe feature.

[Old Smokey]

To reinforce the three respondants, and to put a slightly different twist on the words -

When you accomplish a battery start, the aircraft is basically in the Emergency Power condition. The 'default' idle position is flight idle, that taken up in an emergency power situation. Electrical power is not available from the Battery buses to Engine Idle control. The various 'luxuries', like hot coffee, landing lights, and Ground Idle become available when normal AC power, and DC power from the TRUs becomes available.

[Hudson]

Thanks for the replies. Another question - again a simulator feature. Engine fire warning is actuated by instructor. The overheat comes on immediately (and MC) and it takes 5 seconds before the fire warning sounds (plus light in handle etc).

I understand that this delay between overheat and fire warning is a feature olf old 737-300 simulators. In later version simulators the actuation of the fire warning on the instructor panel causes simultaneous overheat indication and fire warning.

Has anyone else struck this delay feature in the 737-300 simulators you have sat in? I am interested in case it is a defect in the simulator rather than an expected event

[Old Smokey]

Hudson,
I understand that this delay between overheat and fire warning is a feature olf old 737-300 simulators. In later version simulators the actuation of the fire warning on the instructor panel causes simultaneous overheat indication and fire warning.
The old 737 simulators, and many other old (and some new) simulators still do the same thing. What the simulator programmer has tried to do is to replicate the real world situation. Consider the fire, temperature is rising, not in a microsecond, but over 5 to 6 seconds - real life. The Overheat warning, with a lower temperature threshold will trip first, and, as temperature rises further, trips the fire warning at it's much higher threshold.

This has always been the simulator instructor's problem, timing of an event - I want it, and I want it now! You want to give the student a fire just before V1, for example, and the damned thing goes off after Vr.

In several simulator calibrations / acceptances that I was involved with, we managed to cajole the manufacturer's technicians into 'instantifying' (is that a word) various scenarios such as this, so that the instructor could introduce the fault at the appropriately timed moment.

A check of the "Fault Description" should reveal the programmer's intention, maybe your own sim techs can 'engineer' a bit of deception.

I well remember that loss of oil pressure was one such problem, the programme reasonably caused the oil to leak away, quantity steadily dropped, temperature slowly rose, and finally, 2 to 3 minutes after takeoff (when you wanted it before V1) the oil pressure finally failed.

Sometimes.....Ya gotta cheat a bit.

[Hudson]

Thanks Old Smokey. Very good reply. Regarding cheatin' a little, one of the simulator buttons is for turbine seizure. The 737-300 event mkaes a hell of a racket with the sim shaking and shivering until the engine grinds to a halt. Usually people just let the engine destroy itself as the whole things stops within 15 seconds or so anyway. One way to to check the pilots airmanship side is to drop the engine oil contents after lift off to zero and watch the reaction when the engine starts to vibrate and tortures itself to death over the next minute or so.

My observation is that a surprisingly large number of pilots watch the result with growing interest yet do not step in immediately and shut down the engine. Then when it is all over bar the shouting they call for recall Items Severe damage. The more astute recognise an impending problem and quickly close down the engine well before it seizes. The latter is more desirable I would suggest.

In the NG, it is my experience that the turbine seizure button event is far removed from the -300 described above and is more like a common or garden flame-out with little noise and vibration.
I wonder why the significant difference between the two types of simulator?

[Old Smokey]

Hudson,

This may seem a very short answer to a your post, but my 'gut' feeling lies in a response to your last line - "I wonder why the significant difference between the two types of simulator?"

Are both types of simulator from the same manufacturer ?, OR

If from the same manufacturer, did the programme come from the same supplier ?, OR

Did the same group of people within your company carry out the acceptance / compliance with CASA ?

The answer/s may lie in there, different strokes for different folks.

I can identify with your student's response to the 'catastrophic' engine failure. Too often we teach procedures (in this case handling an engine failure with it's performance implications and procedures), with a simple flame-out instead of the 'complete package'. Flame-outs do occur, but many many engine failures follow ever increasing indications of engine degredation. In one 'package' which I created, it began with a loud bump (bird strike), compressor stalls, rising EGT, increasing vibration (lost turbine blades), and finally seizure with accompanying very convincing vibrations/shaking. Some of the astute picked it up early, some needed a little more convincing. The slowest learner turned to me and said "why did all the shaking and vibration stop ?". I informed him that the engine could take it no more, and separated from the aircraft. "Oh, he says, good then, the problems gone". So too, was his base check.

Regards,

Smokey