B737 Loss of Both Engine Driven Generators

[Judd]

This non-normal is covered during type rating and recurrent training. Scenarios differ depending on the simulator instructor, but usually involves a failure of one engine driven generator while airborne followed soon after by the second engine driven generator. A lengthy non-normal checklist follows. Once that is completed, an instrument approach (with limited flight instruments in some aircraft) and landing completes the exercise.
There have been documented cases where a lightning strike affected the electrical systems including failure of an engine driven generator. On one occasion when the crew attempted to restore the faulty generator, that action caused the second generator to fail, leaving for a short while loss of both engine driven generators. All this takes place while airborne.

In the case of the 737 Classic for example, a double generator failure during the take off roll presents an entirely different situation than an airborne double generator failure. At night, the flight deck goes to total darkness including all instruments. Partial lighting can be restored by actuation of the Standby Power switch to ON but the PM has to be quick and know instinctively the position of that switch in a darkened environment. The flight/ground logic is disturbed which can result in false aural signals such as the takeoff warning sounding while the aircraft is still rolling and erroneous stick shaker operation at rotation. Once airborne, the flap indicator is inoperative as well as the electrically operated stabiliser trim switch.

Last, but by no means least, rotating on and subsequent flying on the standby ADI and using the RMI as a compass brings its own challenges. Loss of the inboard Anti Skid system means a high speed abort would likely cause the inboard tyres to fail and thus partial loss of braking capability. It is generally safer to continue the take off and sort out the problem at leisure when airborne rather than risk an over-run if on a runway limiting take off with loss of partial anti-skid.

The above scenario paints quite a dramatic picture and coping successfully takes considerable flying skill and good airmanship. Despite this, one rarely sees this non-normal practiced during type rating or recurrent simulator training. The danger is not the airborne part; but where the proliferation of false warning signals and the surprise factor leads the pilot to unnecessarily abort the take off

[RAT 5]

I take your point about RTO-ing, and much might depend on day or night and weather conditions on departure, i.e. cloud base and vis for a return; also the length on the runway. RTO-ing does not necessarily mean max braking until a full-stop. So declaring it always an unnecessary RTO might be a little over simplifying a complicated scenario.

Because of all the aspects you mention giving this double failure on takeoff during a TR course is much too complicated at an early stage of training. During an RST as a pure confidence building and educational event is the correct stage, but because it will take a long time to complete with quality I doubt it features in many airlines programs. In my experience of various training syllabi the total AC failure (or double gen failure) is treated as so unlikely that it is often just a pure demo and discussion. Some allow a raw data ILS so two boxes can be ticked at the same time. What is missing is SBY instrument training. On NG it is a customer option, or was, to have PFD on SBY AC, thus a real small SBY ADI approach is not trained nor experienced. To me that is a gap that needs plugging. Some will argue it takes too many multiple failures to arrive in that situation, but it is a great confidence builder to fly such an approach. Great hand eye coordination and full understanding of Power/ATT control.

[Pugilistic Animus]

No RAT/PTU/HDG? Just curious

[tdracer]

No RAT/PTU/HDG? Just curious

No RAT on the 737 (disclaimer, not completely sure about the MAX) - you don't need hydraulics to fly the 737 (although it sure helps). Battery is supposed to supply critical flight instruments for at least 30 minutes after a complete loss of electrical generation. I don't think you can enter an ETOPS sector with a failed engine driven generator (I stand to be corrected here - I'm not that familiar with the 737 limitations).
Note that this arrangement was pretty common on the earlier generation of jet aircraft - even the 747 didn't have a RAT prior to the 747-8 since in an all engine out, the windmilling engines would provide enough hydraulic pressure to control the aircraft (granted it takes more failures on a 747 to get there).

[RAT 5]

EDP's still working. No problem with flt controls.

[BluSdUp]

I only have experience with the 737-800, but it is a non event.
Cpt becomes PF as his PFD and MFD and Upper DU is the only ones working. AT off, as AP has gone. Manual pitch trim.
Descend and start APU.
Engine driven pumps keeps the hydraulic at a happy 3000psi ( Not to be confused with manual reversion ,TD, as that is something You for sure will remember on a dark and stormy night!!)
Flaps and gear drops normal.
What more does a man want!?

[tdracer]

RAT/BSU, I guess I wasn't clear - I was referring to the dual engine power loss (not dual engine electrical power loss - subtle but important distinction). 757/767/777/787 have (need) a RAT to provide sufficient hydraulics for flight controls, 737 doesn't need it since it can be flown without hydraulics.
I don't think any airliners need a RAT for dual engine electrical power loss.

[BluSdUp]

TD
Indeed,yea, lets call manual reversion on the 737 " Can be flown without hydraulics" if the sim is anything to go by. Mind you I suspect it is tweeked a bit on the hard side in the sim.
Nevermind.
The 787 , how is it doing without engine and apu generators. Does not the Rat supply any elec TD, as I understand it has next to no hydraulics?
Off tread, sorry!!

[tdracer]

TD
Indeed,yea, lets call manual reversion on the 737 " Can be flown without hydraulics" if the sim is anything to go by. Mind you I suspect it is tweeked a bit on the hard side in the sim.
Nevermind.
Hey, I never said it was easy to fly the 737 without hydraulics - just that it was possible (although a whole lot easier to fly without hydraulics than most jetliners).
The 787 , how is it doing without engine and apu generators. Does not the Rat supply any elec TD, as I understand it has next to no hydraulics?
Off tread, sorry
The 787 still has some hydraulics - although the systems operate at 5000 psi (rather than the more typical 3000 psi) which means the hydraulic components can be smaller/lighter for the same muscle. However I believe the 787 RAT has both a hydraulic pump and an electrical generator - that's the way the 777 is configured (although with 3000 psi hydraulics). I have limited first hand knowledge of the 787 - never worked the program - the only current Boeing aircraft I never worked on.

[Jwscud]

You get 60 minutes on the 737 battery on the EASA model. I once did a ferry of a 738 with lightning strike damage on a single AC source under a ferry permit. You may imagine we had a long hard read of that checklist before departure, and options were never far from the front of our minds!

[EEngr]

...Partial lighting can be restored by actuation of the Standby Power switch to ON but the PM has to be quick and know instinctively the position of that switch in a darkened environment.

Not a 737 power system expert (more experience with 747 and 767), but wouldn't the Standby Power switch be placed in Auto (or Bat) as part of a normal startup sequence? There isn't an 'On' position to be precise. In Auto, the loss of all AC generators would result in Standby AC and DC loads being supplied by the battery (and inverter) automatically. For hopefully enough time to get the generators sorted out.

[Judd]

but wouldn't the Standby Power switch be placed in Auto (or Bat) as part of a normal startup sequence? There isn't an 'On' position to be precise.
Correct. My error. If double generator failure (no APU ) occurs on the ground during the take off roll the Standby Power switch on the 737 Classics should be switched to BAT

[IFixPlanes]

...At night, the flight deck goes to total darkness including all instruments. ...
That is not correct.
The left dome light still works because power source is dc battery bus.

[Banana Joe]

Not a 737 power system expert (more experience with 747 and 767), but wouldn't the Standby Power switch be placed in Auto (or Bat) as part of a normal startup sequence? There isn't an 'On' position to be precise. In Auto, the loss of all AC generators would result in Standby AC and DC loads being supplied by the battery (and inverter) automatically. For hopefully enough time to get the generators sorted out.

Not on the Classic. On the ground the AC and DC standby busses are not powered with the STANDBY POWER switch in AUTO to prevent battery discharge. The switch must be placed to BAT to power those busses.

[Centaurus]

The left dome light still works because power source is dc battery bus.

Does that still apply with the aircraft on the ground with loss of both engine driven generators? Or if airborne only?

[Banana Joe]

It depends on which 737. As you can read in my previous post, on the Classic the STANDBY POWER switch must be placed to BAT to power the standby busses on the ground. Not needed on the NG.

[IFixPlanes]

Does that still apply with the aircraft on the ground with loss of both engine driven generators? Or if airborne only?

There is a difference between standby bus and battery bus.
Bat bus is powered when Bat SW is on - no matter is ground or air.:ok: