To have a backup ASI/altimeter?

In the interest of stimulating discussion on panel logic, this is something I don't understand. Modern EFISs are very reliable, I don't know the precise failure rate but if we could see the numbers I think we'd see that it's about as probable as your engine quitting. I'd bet that most of you still building will have a GPS in the panel also and there's a good chance it will be a Garmin 396/496. If so then the GPS provides groundspeed, GPS alititude, and even a mock instrument panel. The Garmin also has built in battery back-up. Should the EFIS ever go down, either by failure itself or failure of the ship's entire electrical system, just use the GPS to fly to the nearest airport.

So, here's the question for debate: why add the expense, weight, and complexity of backup ASI and altimeter on a VFR-only aircraft? Thoughts & opinions?

I'll put my 2 cents in here - many many years ago when I learned to fly my instructor spent several hours teaching us to fly with all the instruments covered. We even shot vfr night landings with no landing lights or instrument lights. His basic idea was to learn to fly the airplane by feel -

I remember being very nervous at the time - but eventually - I had to land at night at an airport with no landing lights, or any runway lights. Sure was glad to have had the training.

Come to think of it - it's probably time again to go out and fly for a few hours with everything covered up. We started with basic stalls etc.

I installed a backup ASI/Altimeter on mine. I am using the MDL EFIS with no further avionics.

I am also adding a backup bubble.

I figure that I will be concerned enough if I lose an EFIS (unlikely - but certainly possible) that I want enough instrumentation for me to get on the ground without guessing at airspeed/altitude/slip. I will probably see this as unnecessary later, but I will never know because mine will have it.

Tom L
SS7 - 912 ULS - in progress.

I saw an A220 at a fly in and really liked the layout. I also added the 496 you mentioned and an altimeter and VSI I had laying around. EFIS is a GRT Mini AP. Pics on show your panel page.
I like the way it turned out so far. I have redundancies that I probably will never need but I like it.
Weight - I'm guessing 99.5 percent of the time it will be just me and gas... er... fuel

I am pretty much in the same camp as Rodney from OK (in addittion to having a nose gear KF) - train with the instruments covered (standard gauges or glass) till a person gets good at it. If a person knows what horizon angle the wing assumes at a particular airspeed - you can come pretty darn close - certainly close enough that there is no danger of stalling and minor concerns with a longer roll out....heck, if a kitfox doubled a rollout.....it would still be shorter than most other aircraft.

If considering an uncertain short strip - a practical strategy might be to go to a different airport if it is really a concern.

Agreed - failures of this equipment (ASI & Altimeter) probably don't happen too often - if the ASI messes up - old tech or new tech.....it will probably be caused by a low tech problem - bug or lump of something impacting the pitot.

The GPS groundspeed is still useful information for estimating airspeed - Prior to landing - Nothing to keep a person from experimenting with flying upwind and downwind directions for the runway to be used a distance from the airport at pattern altitude - take half the up/downwind groundspeed difference for the wind effect aloft and add that to the GPS groundspeed for a fair estimate of actual airspeed on final approach.

Actually - the GPS has lots of uses other than basic navigation.....I have found it useful to figure out gust & shear factors before landing when there is an extremely large wind gradient between pattern altitude and the surface.

Good topic Randy,

GPS has made the loss of basic flight instruments a non-event. I just finished a new instrument student and we did several partial panel approaches in prep for his check ride. With a simulated loss of pitot static, the GPS gives altitude, direction, rate and ground speed. That's way more backup than we had back in the 70's with a "fully equipped" IFR panel. But there is a catch.

The role of the basic 6 pack of instruments has morphed into back-up status with GPS and glass panels becoming primary. We used to think loss of vacuum was the scariest failure. Now it appears to be loss of electrical. So the question on partial panel is now, "Do we need a backup for the glass panels?"

The problem is the integrated units are all or nothing electrical boxes. If you are flying with a Garmin 530 and it dies, you lose nav, com, and transponder. If you use a primary flight display like a Dynon or Aspen, and it dies, you lose a lot more than just one or two gyros. With GPS and PFD's we must carry as backups the very instruments we wanted to eliminate.

So do I need (or simply want) a backup altimeter for my experimental airplane that flies only VFR? Probably not... I've got all the info I need on my cellphone.

I haven't tried it yet, but I'd like to see if I can fly a simulated GPS approach with just a cellphone app.

John Pitkin

The iPhone backup assumes you have loaded the proper maps, etc beforehand or that you have cell coverage. Inclusion of an AS/Altimeterinstrument on a separate breaker/switch is very inexpensive and easy to implement

I have a short strip 900' with obstacles. I can't remember the last time I looked at my airspeed on final. Flew all last summer with my airspeed covered. I like to fly off airport a lot and if your looking at the panel on final you might be missing something more important in front of you. I think everyone should be able to fly vfr without gauges if you can't go practice until you can. Losing your asi should be a non event.