Which gauges should stay "old school" in a glass cockpit

[Ironflight]

Originally Posted by N355DW

I believe you, this was back in the nineties and I am well out the airline loop now. I guess my point is to have a few critical instruments that have independent systems, and I am unfamiliar with the Gemini, so that is worth checking out. Old fashioned I may be, but I would prefer a mechanical oil temp and pressure, and altitude and airspeed. Perhaps the backup attitude gyro could be electric, not sure I want to install a vacuum system for one gyro, but I would want a dedicated battery and separate wiring system for it alone.

Welcome to the new world - and the new way of thinking. It's not about "having vacuum", or even having "mechanical" systems - smart design is about knowing what functions are critical for a given operation, and making sure that you have at least one backup plan to provide that function. And, of course, you need to be honest about your real redundancy....yes, that means redundant electrical back to the source if you depend on electrical instruments.

Instruments/avionics/systems are the fastest-advancing part of experimental aviation.

[wolfpack21643]

Funny story about a full electric out situation. My Sheriffs Office got a brand new Savannah VG STOL airplane from the Feds. I went and picked it up had a 1 hour check out flight with the ferry pilot and was cut loose to fly it back to our home field solo. No problem. Then the next day our radio guy came out to the hanger and set up the police comm. on the airplane. He wanted to go up and check out how it worked.

On the taxi out he made the comment that he had never been in any kind of airplane before in his life. We took off and I could tell he was extremely nervous but he assured me that he really wanted to take a flight. After about 10 minutes of flying I lost all of the electric. And I mean all of it. We had a back up battery system and guess what, we lost that to. The airplane was all electric so I lost the flaps, trim instruments the whole nine yards. I had logged a total of about three hours in it. The plane uses the Rotax 912 which at the time I knew nothing about.

I held my breath that the fan would keep spinning and turned back for the airport. When the EFIS went out my passenger got so scared that he tossed his cookies all over the front of himself. To say that my stress level was high is an understatement. I had a total of 2 landings in the plane and now I had no flaps, instruments or trim. My passenger was so scared that he actually tried to rip the stick out of my hand and take over control of the airplane when the airport came into view.

I let him take the stick and I crossed my arms, looked at him and said ?I got 4000 hours in the air what you got?? He let go of the stick and started to hyperventilate. I shot my approach hot and set up to sit the airplane down on the 1000 foot marks. We floated because of the extra speed I was carrying but still made a nice soft landing before the end of the runway. As soon as I pulled up in front of the hanger he opened his door fell out onto the ground on his knees and tossed the rest of his lunch.

Come to find out the ignition switch melted down and the back up battery system wasn?t wired up right from the factory. If I had a few working steam gauges I could have calmed my passenger down a lot. I could have pointed to the ALT and AS and said ?ALT and AS are a pilots best friend? . He told me later that when we lost everything he couldn?t help thinking that I would get lost and such without the GPS and gauges. And that the airplane would catch on fire or something. A non pilot is pretty clueless to what?s going on up there.

Believe me if that?s all it takes to make a non flying passenger feel better in an emergency then it?s a small price to pay because he took my stress level from a 3 to a 10 when he started getting sick and trying to take control of the aircraft. My RV 8 will have a back up steam AS and ALT.

[N355DW]

Originally Posted by Ironflight

Welcome to the new world - and the new way of thinking. It's not about "having vacuum", or even having "mechanical" systems - smart design is about knowing what functions are critical for a given operation, and making sure that you have at least one backup plan to provide that function. And, of course, you need to be honest about your real redundancy....yes, that means redundant electrical back to the source if you depend on electrical instruments.

Instruments/avionics/systems are the fastest-advancing part of experimental aviation.

Well, don't welcome me quite yet! It may be about "smart design" these days, but if I have a pitot and static line connected to an altimeter and airspeed indicator, it seems like adding an unnecessary layer to then hook it up to something that requires electrons for me to interpret the data. Another layer that can malfunction.

Don't get me wrong, I am a technophile as much as most pilots are, and love the new gadgets. I am quite comfortable learning new technologies and using them. I'm going to put the best I can afford in mine, and in many ways it will out do the cockpit of every airliner I have flown, I am quite sure. But while I love all the gadgets, I am very aware that each and every one is just another fancy toy that can break or just mess up. Electronic toys with computer chips especially. I will never put all my trust in them, no matter how many there are, especially when for very little money I can have a simple mechanical back up.

Great discussion, I am learning a lot! I am very glad I joined this forum, the things I learn here will no doubt help me to build the best plane I possibly can.

[pierre smith]

I'm getting used to my "glass cockpit" as well. I learned back in '67, so yeah, I'm old school too.

A well thought out dash can be really sweet, with steam gauge backup. The guys that built my -10 did a great job:



The 'round' AH is my autopilot but functions as a very good artificial horizon.

Best,

[Toobuilder]

If your primary mission is day/vfr, then I think I could get away with only an oil pressure idiot light as my backup. In the unlikely event of total electrical failure, ASI or altimeter are not needed as long as you can look out the window. In fact, I have a friend who is so glued to the panel in flight that lately I have been turning everything off and covering the steam gages to force him to look outside. It's amazing how quickly your other senses take over when you have to feel/listen to the airplane rather than simply drive by some numbers on a screen.

If you're day/VFR, I consider "primary" instruments as simply "pilot aids"... sight picture, sounds and feel come first.

[Doug]

Originally Posted by Toobuilder

ASI or altimeter are not needed as long as you can look out the window.

Nope... Alt is critical in the modern airspace, and ASI impossible without other instruments to cross check.

Vibration is the enemy of electronics, and an airplane is the single worst environment according to the mil spec mtbf figures. You are expecting the manufacturer to have undertaken a risk assessment in the design process, and designed out any weaknesses.

I expect most major manufacturers to have been responsible in their design process, but in a commercial environment with a few niche manufacturers this may not be the case. This is too big a risk for me so I have a back up Alt and ASI.

Doug Gray
20 years as a defense contractor in the supply of mil electronics.
RV-6 flying

[Toobuilder]

Originally Posted by Doug

Nope... Alt is critical in the modern airspace, and ASI impossible without other instruments to cross check...

Perhaps we look at "critical" differently. To me "critical" means "if you lose it, you might die". If you define critical as being able to press on with the mission, then I'm more inclined to agree.

However, since I can fly around just fine (day/VFR) without even looking at the panel, this does not even come close to a critical instrument for safety of flight.

[Ironflight]

Originally Posted by Doug

Nope... Alt is critical in the modern airspace, and ASI impossible without other instruments to cross check.

Vibration is the enemy of electronics, and an airplane is the single worst environment according to the mil spec mtbf figures. You are expecting the manufacturer to have undertaken a risk assessment in the design process, and designed out any weaknesses.

I expect most major manufacturers to have been responsible in their design process, but in a commercial environment with a few niche manufacturers this may not be the case. This is too big a risk for me so I have a back up Alt and ASI.

Doug Gray
20 years as a defense contractor in the supply of mil electronics.
RV-6 flying

OK, I respect that you have years of experience with Mil Spec electronics. What experience do you have with the modern GA, experimental avionics systems? I have quite a few years of flying behind numerous manufacturers devices, totaling thousands of hours - and I have traded notes with thousands of other pilots here and elsewhere in the experimental world. While I have seen failures in the new EFIS's, none of them have been directly attributable to vibration.

For those who are worried about the loss of airspeed indication, as long as I have a single Pitot tube, I have the same vulnerability to loss of airspeed as those with a steam gauge. And I am with those who define critical as "if it fails, and you have no backup, you will die". I certainly don't put airspeed in that category for VFR, and for IFR, I have been flying around with a single Pitot tube for decades.

[bizjet]

Nice thread. Since I have a bit of experience with the subject, I thought I might offer my $0.02 worth. You get what you pay for.

I flew strictly steam from 1960 to 1986. Flew mixed and combination of steam and glass from 1986 to 1996. All glass since 1996.

If I ever update my panel it will be pure glass. The only way to fly. I think that a vacuum pump is the sorriest thing ever put on an airplane.

In addition, as has been mentioned, if you want true redundancy, you must have two pitot and static sources.

YMMV.

Regards,

Bill

[humptybump]

First, thanks to everyone for posting your thoughts and experinc as it relates to redundant systems and backups for flight instrumentation.

On one point brought up above, I want to pass along my own experience ...

I have first person experience with vibration related failure.

My autopilot started failing and throwing errors on a recent flight. It's not "current" so it was not under warrentee and not worth the $1000 to have the manufacturer bench it (given i was already planning an upgrade).

I opened the unit, re-seated all the boards and it's working fine once again.

So, I have at least one experience with vibration causing electronic avionics to fail. While it may not be common, it can and does happen.