Bryan and "no name" ask:

<< How would the lack of accurate airspeed indications make the attitude
 indications of the Chelton system not reliable?>>

<<What I don't get is why the airspeed would get more attention than the EFIS which would presumably say you are straight and level.>>

It is NOT the hardware. It IS the pilot. The display was accurate (I have the data that shows that) but the pilot did not believe or understand it. A trusted standby instrument may have focused attention away from airspeed. You must consider the totality of the situation, NOT just individual displays or sensors. You are flying along and you hear the "STALL, STALL" Bitchin' Betty audio warning. You CONFIRM that a stall is imminent by looking at the airspeed tape. Yep, it is low. You crosscheck your standby and it agrees with your primary. You believe you have three pieces of information that all agree, because they do. You fail to recognize that all three are the result of a single inaccurate sensor. There is no direct "you are not stalling" indicator. You must infer your actual status from your attitude, engine power and airframe status (flaps, gear, ice) and because that takes significant mental effort you react by lowering the nose. What can it hurt? You will "fly the airplane" and then diagnose the problem.

When lowering the nose does not fix the problem you are surprised and you fixate on that problem. You are stuck in a "fly first , diagnose later" do loop. You stop flying the airplane and start flying the airspeed. It is a fatal mistake. It is not uncommon. Airliners have crashed because of it. A standby AI in the scan would have emphasized the attitude status.

Most AHRS systems synthesize attitude information using accelerometers, and rate sensors. Typically the accelerometers have an internal beam element (diving board) that deflects due to the forces induced by gravity and acceleration. Rate sensors measure rotation rates and use a vibrating beam or ring to measure the Coriolis forces. Both types of sensors are not perfect and have drift. In order to maintain an attitude indication with good fidelity to reality you must "aid" the attitude with magnetometers, air data and / or GPS.

Gyroscopes operate on the principle of of conservation of angular momentum which produces "rigidity in space" of the spinning element. The gyro display shows the difference in alignment between the spinning mass element and the AI housing. The gyro also has aiding in the form of balance weights that erect the gyro to the apparent gravity vector. In a turn the apparent gravity vector is the vector sum of the gravity vector and the centripetal force of the turn. This is why when you stop a long duration turn your roll attitude indication is off.

Gyroscopes and AHRS use different physics to do the same thing so if they agree then you are probably looking at the truth.

In the comfort of your computer chair you can calmly and rationally consider a serious situation and you will usually  arrive at the correct remediation. Can you do the same trick in a room that is on fire during and earthquake when you are seeing and hearing conflicting information, you know your life is at risk and you are amped up on adrenaline? Can you make the right decision in 20 seconds?

You best chance for survival is to have your primary and standby instruments IMMEDIATELY available and part of you normal scan. You also need to train, train, train with a competent instructor who focuses on unusual and emergency situations.

Statements like "Little plastic home made airplanes do not belong in hard IMC conditions even with a big engine and piles of expensive avionics!" expose an all too common combination of ignorance and arrogance that manifest as a "blame the hardware" attitude. The data is unequivocal, it is the pilot, not the hardware at the core of safety. Blaming the hardware focuses attention away from the true problem. IMHO pilots of that school are the most likely to suffer ego related fatalities.

I have extracted flight information from six crashed aircraft. in all cases the accident was the result of poor pilot decisions. None were a direct result of a mechanical failure. I am sure that each of these poor souls was just as confident as you that it could not happen to them.

"Can't happen to me" you say? Bullshit!

This accident investigation stuff is not fun.  The picture below is of a recovered Chelton display (no, I won't identify the aircraft). Wearing double gloves, surgical mask and safety gasses I had to dig through the broken glass and rotting biohazards to extract the flash memory ICs that contain the flight log files.  After this I analyze the intimate details of the last moments of a member of our fraternity and draft a factual report for the investigators.  I do this gratis. If you don't know why then you won't understand an explanation.

I can say with experience and grim confidence that someone reading this post will be dead due to an aircraft accident within the year. That accident will be the result of poor builder / pilot decisions. Having the thoughts like "not me" or "the hardware will keep me safe" puts you at the top of the list.

The Naval Aviator's saying that "everyone is trying to kill you" applies to the PIC as well. Humility and fear my friend, humility and fear.

Regards
Brent Regan