B737-300 Standby ADI power failure due dual engine flameout and defective battery

[A37575]

A recent Rumours and News thread (since disappeared?) discussed the dead stick (double flameout) of Garuda Indonesia Boeing 737-300 Flight GA 421 on 16 January 2002. While descending through 18,000 ft the aircraft entered a thunderstorm which caused both engines to flameout due rain ingestion.. An attempt to start the APU was unsuccessful due to a battery defect. Attempts to re-light the engines were unsuccessful as the aircraft was still in heavy rain and the aircraft made a forced landing wheels up and flapless.

The battery failed at the moment the crew tried to start the APU and this left them with not only a double engine failure but no electrical power.

The aircraft was IMC when this happened and the crew were fortunate to become visual soon after. I was wondering if someone could advise how many minutes after a total electrical failure (meaning nothing including battery power), would the standby ADI be usable before the its gyro ran down to where the ADI would topple or be useless.

In the case of the Garuda Flight GA 421 incident which occurred in cloud, there must have been sufficient run-down time for the standby ADI to give reasonably accurate pitch and roll info with no power to the gyro. This is not mentioned in the Indonesian accident report yet it would be good for pilots to know how long they have before the standby ADI fails to give meaningful information after electrical power is removed from it.

[BOAC]

Are you certain it was a 'mechanical gyro' instrument? I'm pretty sure L Ring standbys were around in 2022 in which case I reckon the loss would be instantaneous. Even if 'mechanical', depending on the way the gyro attitude is 'passed' to the instrument face it could be instantly 'dead'. A lucky break indeed with the weather.

[A37575]

Are you certain it was a 'mechanical gyro' instrument?..

No - I am not certain. The FCOM does not mention this either - at least not the copy I have. I tried it in the simulator and found that pitch and roll worked OK but I only did it for one minute so didn't prove anything.

[Checkboard]

The standby ADI (or ISFD (Integrated Standby Flight Display) after 2003) have their own, integrated, battery supply. They are only connected to the standby power system to recharge that battery - so the failure of the aircraft batteries wouldn't affect the standby instruments.

[SR71]

Well I never knew that....not that I'm planning on flying around on STBY instruments in the near future....

But it does beg the question, how long do THOSE batteries last?

Curiously.

[Checkboard]

Interestingly the ISFD cannot be switched off from the flightdeck - even by pulling the ISFD c/b on the p18 panel. It has its own dedicated battery and the ISFD c/b only removes power from the battery charger, so let us hope that one does not start to smoke in-flight! The battery will give 150 mins of power.

Boeing 737 Flight Instruments (http://www.b737.org.uk/flightinsts.htm#Standby%20Flight%20Instruments)

[Denti]

There is no retrofit for classics for those as far as i know though. Might be mistaken there of course. In a classic (-300 to -500) it would have been most probably a normal mechanical gyro which does not have as far as i know any guaranteed time after a complete battery failuere where it provides reliable attitude information. Even the early NGs don't get retrofitted with an ISFD as far as i'm aware, on the latter ones it is standard equipment and actually mandatory for fail operational autopilot ones (provides third attitude reference for the autoflight system).

[Checkboard]

Yes, a battery operated electric gyro. It isn't much of a "standby instrument" if it fails when the power goes! ;) An independent source of electric power (i.e. its own battery) is required by the regulations.

Avionics Magazine :: Standby Flight Instruments: Helpful or Hazardous? (http://www.aviationtoday.com/av/issue/feature/Standby-Flight-Instruments-Helpful-or-Hazardous_12603.html)
In the MD-11, small standby attitude, airspeed and altitude instruments were located side by side at the bottom of the center instrument panel, above the power levers. A retractable compass at the top of the windshield, to the left of its center pillar, provided standby heading.

Under regulations, only the attitude indicator was required to have independent power.

[Denti]

Remember when the 737 was certified. Digged out my old -300 manual and it says:

The standby horizon indicator provides attitude information that is independent of the primary attitude displays. The indicator is powered by the battery bus and remains powered after the loss of all normal AC power as long as battery power is available. The gyro reaches operational speed approximately 60 seconds after power is applied. The indicator requires three minutes to achieve accuracy requirements.

The following list identifies the significant equipment that operates when the battery is the only source of electrical power and is powering the standby busses.

Flight Instruments
• clocks (hot battery bus)
• standby airspeed/altitude indicator
• standby horizon indicator



No individual battery pack i'm afraid, that's something only the ISFD has on the 737 series, 150 minutes battery power as said above. You gonna notice when the battery is gone anyway as the display blanks.

[Checkboard]

Hmm, bit more research, then:


(j) On the airplane described in this paragraph, in addition to two gyroscopic bank and pitch indicators (artificial horizons) for use at the pilot stations, a third such instrument is installed in accordance with paragraph (k) of this section:

(k) When required by paragraph (j) of this section, a third gyroscopic bank-and-pitch indicator (artificial horizon) that:

(1) Is powered from a source independent of the electrical generating system;

(2) Continues reliable operation for a minimum of 30 minutes after total failure of the electrical generating system;

(3) Operates independently of any other attitude indicating system;

(4) Is operative without selection after total failure of the electrical generating system;

(5) Is located on the instrument panel in a position acceptable to the Administrator that will make it plainly visible to and usable by each pilot at his or her station; and

(6) Is appropriately lighted during all phases of operation.
Needs a battery, but that can be the ship's battery then.