Instrument requirements

[coless1]

Being new, I apologise in advance if this information is available somewhere!
I will be building a Eurofox. I prefer round dials, but I have to compromise because I want a Horizon as well. One way to achieve that is by a Dynon D6 or 60, which would provide AH and a lot more besides (ASI,VSI,ALT,Hdg etc.). My personal view is that all I really need by way of backup is a nice big analogue ASI and an altimeter. I don't need a VSI or a slip ball and the heading, or at least track, would be available on a separate, independent map. But I am told an analogue VSI may be a required instrument. Is this true? If so why? My 'other' aircraft is a share of an SR20; that is all EFIS, of course, and certificated, with the only backup flight instruments being ASI,AH,ALT, ie NO VSI. Could somebody point me in the direction of the rules on all this? Who writes them and are they reviewed in the light of technical development?

[Ian Melville]

Hi Stephen,
CS-VLA is the document you need, Treat the failure of the EFIS as though it was not there
I have extracted the relevant part here

CS-VLA 1303 Flight and navigation
instruments
The following are required flight and
navigational instruments:
(a) An airspeed indicator;
(b) An altimeter;
(c) A magnetic direction indicator

You can have any size you like. I am wishing to do something similar, but have found small traditional instruments very limiting in speed range etc, so will be looking into using MGL Electronic gauges (ASX-1), where one can do both ALT and ASI. It has a backup battery so can still run OK if the power supply is provided correctly. Yet to run this pass the LAA Engineering. It's also cheaper and lighter than steam driven stuff.

Cheers

[Mark A]

If you want ultra light weight electronic instruments, take a look at Belite.

I suspect that the LAA may require purely mechanical instruments to meet the minimum requirements.
That is currently the case for people with expensive EFIS set-ups even though they have battery back-ups.

[ian herdis]

Hi, Stephen

As you prefer round dials you should look at the Tru Track EFIS as it has the info displayed with a traditional analogue type display instead of the usual tape style.

There are smaller back ups available but as the size goes down the price goes up!!!

Ian

[Ian Melville]

I suspect that the LAA may require purely mechanical instruments to meet the minimum requirements.
That is currently the case for people with expensive EFIS set-ups even though they have battery back-ups.

Hi Mark, Did the LAA actually say they must be mechanical?

No matter how expensive an EFIS you have it will need an alternative system. It is not just about power supply, but also software issues.

[coless1]

Thanks, everybody, I am clear now. I need ASI,ALT,Compass backup. That is fine with me, and I have a good idea how I will achieve that.

[Mark A]

Did the LAA actually say they must be mechanical?

I've not personally asked (yet). There isn't an LAA TL on the subject and CS-VLA does not seem to exclude electronic instruments.

For a VFR aircraft, losing instruments due to electrical failure is undesirable, but not critical.

I suspect that they would ask for those 3 (Alt, ASI & compass) to be mechanical, but can't quote chapter and verse. I think a non-sensitive, single needle altimeter is allowed if it's a back-up instrument.

[Rob Swain]

Everyone seems to be blaming the LAA for the Glass Cockpit / backup instrument situation.

It's in the design codes that all aircraft have to follow: it's not a 'LAA engineering is being unreasonable' situation.
Cirrus SR22s and all other factory-built glass-cockpitted planes have to have the backups as well. The SR22 has a backup Artificial Horizon (electric - the Cirrus has a backup, battery and generator etc) as well as the Compass, Altimeter and ASI. The Cirrus installation also demonstrates how tastefully these can be integrated into a glass cockpit panel.

As has already been noted above - the mechanical backups are fitted to safeguard against the glass panel playing up in any number of ways: screen failure, software glitches, wiring faults, gyro failure (to name just a few) and not just simple power failure.