dtibbo wrote:With backups I'm still VFR legal in a dark screen; I could continue that flight. Or return home from a cross country.
I get the urge to make improvements, I really do! However, its important to think through these kinds of trade-offs in a comprehensive manner.
What % of the time are you expecting to have your primary instruments fail? (I'd argue its a single-digit percentage...)
Mounting an entirely separate set of backup instrumentation means spending 100% of the time flying around with a bunch of extra wires and probes and electronics and display equipment. That means every flight you're carrying extra weight, dealing with extra current-draw, you have extra maintenance,
and every flight is undertaken with extra failure modes.
Don't discount that last one.
FMEA is not just for things as complex as the Space Shuttle! What happens when one wire comes loose and flops against something else inside your engine compartment? What happens when you add extra components that then rub against each other during flight? What happens when that added fastener or clamp comes loose? The engine compartment of an aircraft is a hot, wet, oily, dirty, noisy, high-vibration environment - something is bound to wear out, wear through, or come loose at some point!
Just like twin engine aircraft aren't automatically safer than a single, more instruments and wiring are not automatically better than a simple, reliable, well-engineered setup.
I'd argue that - if you perform a risk analysis - the time and money would be far better spent on training. Most of the Sonex accidents we see are not due to instrument failure, or due to some issue that a second set of instruments would've caught. I've been reading Sonex accident reports for over a decade now, and the main serious accident causes are (like most of the E-AB fleet) loss of engine power or the classic stall/spin issue. Therefore you are far more likely to get value and added safety by learning to land slowly and softly (without a stall/spin entry) in an emergency.
BTW, I personally think that training in gliders - especially modern gliders - is veru useful in learning how to deal with engine-out situations and slow-flight.
Lastly, remember that Sonex aircraft don't have incredibly long legs. Even with an aux tank you're not likely to be more than ~400-500 miles from home at maximum. In an emergency where you have to land and leave the aircraft somewhere remote, you're still less than 1 day's drive from home. And again, what % of your flights will be venturing that far afield? Most pilots in most airplanes stick within ~100 miles of home for the vast majority of their flights - meaning a "land out" due to a dark panel (or any other nuisance failure) means a 1-2 hour drive.
I'd take that minor inconvenience once every several years in return for saving money, weight, and complexity in my airplane!
--Noel
Posted: Tue Aug 28, 2018 2:16 am