Instruments failed?
There's an App for that!

Reading from the iPhone's and iPad's internal sensors, X-Vision draws a synthetic-vision image of the world, and

1: airspeed indicator (minus any wind effects, since it knows only your ground speed)
2: artificial horizon (based on the iPad's internal gyros, accelerometers, and GPS if available)
3: altimeter (minus any barometric pressure effects, since it is based on GPS)
4: slip indicator (based on the the iPad's internal accelerometers)
5: heading indicator (minus any wind effects, since it knows only your ground track)
6: vertical speed indicator (minus any barometric pressure effects, since it is based on GPS)

As you can see, this is at least an approximate backup of the ENTIRE six-pack panel! Should any of these instruments in your airplane fail in flight, X-Vision will give you at least an approximate backup based on the iPhone's or iPad's internal sensors, plus synthetic vision as well.

In flight, X-Vision receives attitude and position information from the:
=>Levil attitude gyro,
=>Dual XGPS150 GPS,
=>or Bad Elf GPS

But, if you do NOT have those devices, or they fail in flight, then X-Vision will run on the iPhone's or iPad's internal GPS, gyros, and accelerometers to continue to run normally, based on the best approximation of your current attitude that it can get from its' internal gyros and GPS (which we have found to be within about five degrees in pitch and roll for modest maneuvering).

As of this writing, X-Vision has been tested in a Cessna-172, Vans-RV-8, Columbia-400, and Lancair Evolution to 28,000 feet and 375 knots groundspeed.

X-Vision has been tested on the iPad-2, iPad-3, iPad Retina, iPad Mini, iPhone-4, and iPhone-5.

X-Vision requires iOS 6 or later.