Airliners.net

Are the standby artificial horizon and magnetic compass required for certification of an airliner or just a safety blanket added by manufacturers? If they are required, then to what failures do they cater to, that of the basic sensors proper or that of the EFIS subsystems that process and present the data issueing from the sensors? If they are not required, then why not also include a standby airspeed indicator, altimeter and/or VSI and make that safety blanket a little more ample?

Faro

Quoting Faro (Thread starter): why not also include a standby airspeed indicator, altimeter

they do.

Quoting Faro (Thread starter): If they are not required, then why not also include a standby airspeed indicator, altimeter and/or VSI and make that safety blanket a little more ample?

We have a standby horizon, altimeter, Mach number and IAS indicator. So all the basic things you need.

wilco737

In addition, we also have a standby ILS with a FD. The ILS will work on a front course or back course. On the 744 and the 320 you have a flat display that has the standby horizon, airspeed and heading.

Quoting Faro (Thread starter): Are the standby artificial horizon and magnetic compass required for certification of an airliner

I would think so

Quoting Faro (Thread starter): If they are required, then to what failures do they cater to

If the ADC takes a dump.

Quoting Faro (Thread starter): If they are not required, then why not also include a standby airspeed indicator, altimeter and/or VSI

As was said above they do. There is also a function in the IRU, if that goes, where you can put them in ATTitude mode and set the IRS heading in the FMC. That in turn allows you to use the raw data modes EFIS has. It should also bring back the RMI compass card and that is a lot easier to use then the whiskey compass because I don't think it has the turning errors, but I'm not positive on that.

Quoting Faro (Thread starter): safety blanket a little more ample?

Weight/cost vs. ever actually needing them as well as the redundancy built into these systems..

Quoting DescendVia (Reply 4): There is also a function in the IRU, if that goes, where you can put them in ATTitude mode and set the IRS heading in the FMC. That in turn allows you to use the raw data modes EFIS has. It should also bring back the RMI compass card and that is a lot easier to use then the whiskey compass because I don't think it has the turning errors, but I'm not positive on that.

These raw data modes still have the standby instruments' indications routed via the ADC/EFIS or routed directly to the flight deck instrumentation screens? Is there any basic instrumentation that is independent of the EFIS electronics?

Faro

Quoting Faro (Reply 5): These raw data modes still have the standby instruments' indications routed via the ADC/EFIS or routed directly to the flight deck instrumentation screens?

Not sure what you mean but EFIS is those screens pretty much.

All you get in ATT mode is navigation capability (e.g. VOR CDI, DME off the RMIs, NDBs off the RMIs, and a basic un-slaved DG). You have to reset the heading every once in a while because it does drift. You will also still be able to see the route on the EFIS map in PLAN mode only.

Quoting Faro (Reply 5): Is there any basic instrumentation that is independent

Yes everything else. Once in ATT mode both the EADI and EHSI go blank, other then the above mentioned stuff. So you don't have an attitude, altitude, or airspeed indicators on EFIS in ATT hence why the standby stuff is there.

Now don't get the ADC failure and an IRU failure confused. ATT mode would be used in a IRU failure not an ADC failure unless both took a dump, in which you would probably do the same  

Quoting DescendVia (Reply 6): Now don't get the ADC failure and an IRU failure confused. ATT mode would be used in a IRU failure not an ADC failure unless both took a dump, in which you would probably do the same

Thanx for the feedback, I guess what I was trying to figure out is whether the standby instrumentation is independent of electronics (or even electricity) which I gather is not the case. Was thinking of a total electrical failure but then I guess you cannot really have those since you still have the RAT and battery backup.

Faro

[Edited 2009-06-10 05:25:07]

Quoting Faro (Reply 7): I guess what I was trying to figure out is whether the standby instrumentation is independent of electronics (or even electricity) which I gather is not the case

It is quite independent. Older systems have simple mechanical horizon, airspeed and altitude indicators which are directly linked to the third pitot/static system (no computer in the system). The horizon however needs el. power and is therefore only usable for about 5 minutes after electrical failure. Newer systems have a small display (ISIS, independent standby instrument system) instead of mechanical indicators which includes a horizon, speed and altitude scale (and an ILS indication as well). Again there are raw data used for display. There is an internal battery, providing power for about 20 minutes (as far as I remember - could not find the exact figure) in case of absence of aircraft electricity.