A320 designed with FIVE MINUTES backup power to standby AI

TangoWhiskey

TangoWhiskey

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From a July 22, 2008 report (page 4) of an NTSB Safety Recommendation based on an incident this past January on a UA A320 loss of primary instruments at Newark.

I guess they felt their backup electrical systems were robust enough you'd never need more than five minutes of backup power to the standby instruments? This just surprises me. 30 minutes is standard in GA aircraft, and with planes like these operating ETOPS, you'd think a little longer than five minutes would be required for certification...

The Board notes that, in such cases, the standby attitude indicator would remain unpowered and would no longer function if the condition lasts more than 5 minutes. Combined with a loss of primary attitude indication (due to the loss of the PFDs) and degraded environmental conditions, this situation could easily result in the loss of the aircraft.

To address this issue, Airbus has developed an aircraft modification (number 27140) that includes a separate backup power source for the standby attitude indicator. This modification is currently being included on new A320 family aircraft but has not been made available for retrofit on older aircraft. Therefore, the Safety Board believes that the FAA should require Airbus to develop a modification for in-service A320 family aircraft such that, in the event of an AC 1 electrical bus failure, the standby attitude indicator is powered by an additional power source that will last for a minimum of 30 minutes, and require operators to incorporate this modification as soon as possible after it is available.
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TangoWhiskey said:
From a July 22, 2008 report (page 4) of an NTSB Safety Recommendation based on an incident this past January on a UA A320 loss of primary instruments at Newark.

I guess they felt their backup electrical systems were robust enough you'd never need more than five minutes of backup power to the standby instruments? This just surprises me. 30 minutes is standard in GA aircraft, and with planes like these operating ETOPS, you'd think a little longer than five minutes would be required for certification...
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I think there is a little bit of a misunderstanding. From reading this report I can see why. What you need to ask is how long will the instruments continue to function on standby power . This is how Transport category planes are certified. I am not sure if ETOPs changes this but it does require other generating sources. The 5 minutes for an unpowered STBY ADI that is mentioned in the report is a bit misleading because it doesnt make mention of a standby power situation. The report only discuses a #1 AC buss situation. My bet is that with all gens inop you would get an hour. It used to be 30 minutes but in all the newer jets that I have seen it is an hour.
FB
 
They are addressing what would happen if ALL power is removed from the STBY Attitude indicator. 5 minutes of useful info after loss of power is common for most of the mechanical gyros I've seen. This could only happen with a few rare specific group of failures on the Airbus. This is what the fix is addressing. The STBY instrument bus is still powered off the aircraft battery with the loss of both generators under normal circumstances. The APU would also have to be inop for the aircraft to be down to battery power only for any length of time. BTW, I don't think UA uses any of the Airbus Fleet for ETOPS
 
The thing that wasn't anticipated here was a failure mode that left ALL the screens blank and killed ALL the paths from the various power sources to the standby indicator.

Hence the mod for a dedicated backup power source for the gyro.
 
TMetzinger said:
The thing that wasn't anticipated here was a failure mode that left ALL the screens blank and killed ALL the paths from the various power sources to the standby indicator.

Hence the mod for a dedicated backup power source for the gyro.
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That reminds me of the change made to the DA-42.
 
The Eclipse 500 has a similar design, but without the standby instrument. If all their screens go blank then there is no attitude information for the pilot.
 
That's five minutes after both engines/generators, the APU, and the aircraft battery have all died. Pretty rare for all that to happen. And if it did, it wouldn't matter if the AI still worked, because they'd have no flight controls (FBW flight control system).
 
JimNtexas said:
The Eclipse 500 has a similar design, but without the standby instrument. If all their screens go blank then there is no attitude information for the pilot.
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Well the Airbus apparently had known failure modes that would kill all the screens (and it's happened more than a few times in reality).

I'd bet the Eclipse either has a standby (there's a really nifty electronic self-contained AI/ASI/Altimeter for jets) or it doesn't have those failure modes.
 
Ron Levy said:
That's five minutes after both engines/generators, the APU, and the aircraft battery have all died. Pretty rare for all that to happen. And if it did, it wouldn't matter if the AI still worked, because they'd have no flight controls (FBW flight control system).
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I didn't know that about this bird. I've wondered how much backup there was to the fly-by-wire aircraft to even just have control without instrumentation.
 
KennyFlys said:
I didn't know that about this bird. I've wondered how much backup there was to the fly-by-wire aircraft to even just have control without instrumentation.
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I really don't know, but every pilot I have spoken to who flies the 320, professes to be comfortable with its redundancy regime. Perhaps one of them here will chime in on the topic...
 
Keep in mind that what happened to the airbus was NOT a loss of electrical power - they had the power to run the flight controls and such. What happened was a loss of a transmission path from the electrical sources to the displays and to the standby indicators.
 
Ron Levy said:
That's five minutes after both engines/generators, the APU, and the aircraft battery have all died. Pretty rare for all that to happen. And if it did, it wouldn't matter if the AI still worked, because they'd have no flight controls (FBW flight control system).
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The Airbus 300, and 320 series can be landed with complete loss of electrical power. (or so the manual says) Rudder control and elevator trim are still available through mechanical backups to the hydraulics. You however, cannot control the aircraft with complete loss of hydraulics. Engine thrust control is independent of the Aircraft electrical system. I beleive the DHL A300 that landed in Baghdad after being hit with a SAM landed electrical out.
 
Power to the BUS was lost. That's not the same thing as saying the generators/batteries didn't have power to provide. I believe that they hadn't envisioned a failure mode that would leave the bus unpowered for more than a short period of time.

Loss of transmission path is my way of saying that there were sources of electricity available, there was just no way to get the electrons from them to where they were needed, even though other systems had sufficient power.
 
The EMB 145 has 40 min on essesential power (Small battery) you can add 5 more by turning off Pito 3 heat, But the plane has 4 gens + an APU gen, plus 2 large batterys + lots of buses & ways to chain power between them (as Ron hit on)

The other thing is at 300 + kts, you had better be able to find an airport in 5 min :)
 
All the jets I've flown (admittedly not an A320) have had an independent source of power in the form of a battery pack for the standby instruments which had to consist of at least an attitude indicator. The power is not routed through any of the normal busses and the system is meant to stand alone. I thought this was a requirement, and I thought the duration of power to the standby instruments had to be at least 30 minutes.
 
SCCutler said:
Perhaps one of them here will chime in on the topic...
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You talkin' about me? :D

11 years is a long time to remember details. 5 minutes seems like an incredibly short amount of time for a standby attitude indicator. But 5 minutes is plenty of time to get SOME sort of power to the system, provided there isn't some kind of failure that would drop ALL electrical power.

Keep in mind my knowledge is stale to the extreme, but IIRC, the standy attitude is on the hot battery bus and that, theoretically is the last system to go.
 
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