Loss of standby instrument during flight
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The Isfd instrument failure question as posted is bit vague.
I would think you have more chance to have a IRS failure in flight than a loss of all normal AC power(Dual gen failure).
For the "HDG part of the Isfd" to be inop you would need the L IRS (on my fleet) to fail.But the right IRS will provide correct heading info to the right PFD.
In that case as i mentioned the APs wont be available for the flight and if you are in for a long flight id return..
For the "STBY ATTITUDE part of Isfd" you d have to have no AC power at all..as it will work with battery power via the battery bus.(if both gens fail and dipatch with APU inop).
Then we all know we need to get on the ground asap.
If you lose the RMI (ac stby bus powered..), so you have no more AC/DC power, well yes you d need to fly with the magnetic compass for headings..
I would not take off with ANY standby instruments INOP.
As far as i remember flying with the mag compass, during the turn you need to overshoot South and undershoot north.
There are some acceleration errors but i forgot...(maybe flying east and west?)
I would think you have more chance to have a IRS failure in flight than a loss of all normal AC power(Dual gen failure).
For the "HDG part of the Isfd" to be inop you would need the L IRS (on my fleet) to fail.But the right IRS will provide correct heading info to the right PFD.
In that case as i mentioned the APs wont be available for the flight and if you are in for a long flight id return..
For the "STBY ATTITUDE part of Isfd" you d have to have no AC power at all..as it will work with battery power via the battery bus.(if both gens fail and dipatch with APU inop).
Then we all know we need to get on the ground asap.
If you lose the RMI (ac stby bus powered..), so you have no more AC/DC power, well yes you d need to fly with the magnetic compass for headings..
I would not take off with ANY standby instruments INOP.
As far as i remember flying with the mag compass, during the turn you need to overshoot South and undershoot north.
There are some acceleration errors but i forgot...(maybe flying east and west?)
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As ludicrousis as it sounds
- that seems to be ludicrous! Surely the whole point of a 'standby attitude indicator' is to provide attitude information when other systems fail, not to provide heading and not to be 'tied' to one of the systems that might fail. The answer is as cough says - you would have to use a mag compass for heading.
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In many aircraft the standbys are there not just for the posibility of a failure in the main indicating systems but also to cope with the possible situation of total power failure, fire etc i.e. where possibly the crew shut all the main systems down to conserve power. For example it is not much use having 3 IRS, 3 ADCs etc etc working perfectly if all the screens are blank!!
The QRH will have the definitive pointers as to what should be done. Many issues also apply - weather, time of day, aircraft current status etc.
What I would compare it to is imagine during the cruise you discovered that all the fire extinguishers were empty except the one under your seat. There is no sign of fire......but what do you do if one starts?
If you can remove the posibility of ever needing the standby eg remaining in VMC then no problem.
There are now aircraft certified with no standby wet compass. However, they have a separate independent flux detector and indicating system for heading on the standby.
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The good old magnetic compass can be used as a last resort to provide wings level information in places where dip is obvious.
It is most noticeable on a heading of North or South because on these headings if the aircraft is banked the compass will swing even if the heading remains constant. On headings of east or west it will not work.
The reason why in the northern hemisphere "South" is the preferred heading for such a let-down is because when on a heading of South if the aircraft is banked left the compass will indicate an apparrent left turn. This makes it less likely to cause confusion.
On a heading of North when the aircraft is banked left, the compass indicates an apparrent right turn. Can be confusing but I am sure that one could cope if there were mountains to the south!!
On the (magnetic) equator - it isn't going to work so simply resort to the simple = trim out wings level in a slow descent and let go = rely on the aircraft's stability.
or, if cloud base permits-
Enter a sipn in your favourite direction and hold it until you break cloud then recover. Not much chance of overspeeding in IMC there!!
Usual disclaimers about aircraft approved for spinning etc etc etc
The QRH will have the definitive pointers as to what should be done. Many issues also apply - weather, time of day, aircraft current status etc.
What I would compare it to is imagine during the cruise you discovered that all the fire extinguishers were empty except the one under your seat. There is no sign of fire......but what do you do if one starts?
If you can remove the posibility of ever needing the standby eg remaining in VMC then no problem.
There are now aircraft certified with no standby wet compass. However, they have a separate independent flux detector and indicating system for heading on the standby.
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The good old magnetic compass can be used as a last resort to provide wings level information in places where dip is obvious.
It is most noticeable on a heading of North or South because on these headings if the aircraft is banked the compass will swing even if the heading remains constant. On headings of east or west it will not work.
The reason why in the northern hemisphere "South" is the preferred heading for such a let-down is because when on a heading of South if the aircraft is banked left the compass will indicate an apparrent left turn. This makes it less likely to cause confusion.
On a heading of North when the aircraft is banked left, the compass indicates an apparrent right turn. Can be confusing but I am sure that one could cope if there were mountains to the south!!
On the (magnetic) equator - it isn't going to work so simply resort to the simple = trim out wings level in a slow descent and let go = rely on the aircraft's stability.
or, if cloud base permits-
Enter a sipn in your favourite direction and hold it until you break cloud then recover. Not much chance of overspeeding in IMC there!!
Usual disclaimers about aircraft approved for spinning etc etc etc
Per Ardua ad Astraeus
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Enter a sipn in your favourite direction and hold it until you break cloud then recover.
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A 747 can fly on 3 engines from LAX to London...
Now, about this diatribe...
... so I can definitely fly my A340 without stdby instruments.
As with most things in aviation, it depends.
IF it all goes pear shaped (and yes I've had this happen with primary flight instruments...all of 'em) one had better have reliable standby instrumentation...otherwise, up the creek without a paddle might just be the case.
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BA 747 diverted to MAN after fuel emergency. It was destined for LHR however. Engine failure after takeoff from LAX and the crew elected to continue with the flight on the 3 remaining engines.
http://www.pprune.org/rumours-news/1...an-merged.html
http://www.pprune.org/rumours-news/1...an-merged.html
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Sorry Aviophage
I must be having a brain dump as I dont see the connection you are trying to make. You can fly any aircraft perfectly well without the standbys operating (albeit taking off as such, isnt exactly legal) provided, as 411A points out, the primary displays and sensors dont go u/s as well.
Please can you clarify the point you are making for us slower types
I must be having a brain dump as I dont see the connection you are trying to make. You can fly any aircraft perfectly well without the standbys operating (albeit taking off as such, isnt exactly legal) provided, as 411A points out, the primary displays and sensors dont go u/s as well.
Please can you clarify the point you are making for us slower types
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You can fly any aircraft perfectly well without the standbys operating (albeit taking off as such, isnt exactly legal)
For the B747-400, ours define despatch as the point at which the aircraft first moves under its own power with the intention of flight.
Anything thereafter you consult the firstly the QRH then the MEL to consider further implications.
Originally Posted by grounded27
...Yes but it relies on an IRU for heading information on many type aircraft.
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Still true though, however that is usually an IRU which is powered by the standby bus in case of loss of generators and therefore continues to run until the batteries are dry.
