We all take it for granted. Take a peek into any cockpit it is always there: the instrument panel centre piece. Certainly a few light, day VFR only aircraft do not require it, why would it be required? It adds weight, cost to maintain and some will even claim that it dulls seat of the pants flying abilities. But to what limit one is to fly with flexibility, day or night never mind IMC? Sooner than later the horizon / attitude indicator instinctively is a must.
The horizon has been part of the « furniture » for as long as we can imagine. The gyro family from which it comes from has been one of the greatest travellers known to mankind!
I certainly, over the years, did not pay close attention to such a given. The instrument in all its variations is pure applied science benefiting flight safety and efficiency. It is always interesting to observe what colleagues have to stare at for hours on.
The AI is well worth it’s added weight to a light aircraft. It is certainly worth its acquisition cost (for the flight director, ring laser version) to the minimum fuelled heavy airliner landing Cat 3 on an early fall morning in Europe.
Nowadays, many upgrade their panel to modern EFIS displays ranging in all prices depending on how sophisticated one desires to go. Indeed, newer MEMS / AHRS technology allows for no errors on the instrument along with lightweight and phenomenal functionalities. None of those pesky accelerate get a climbing turn error exist. Those errors were good to know for licensing exams. Really, I never paid attention to them otherwise.
In the end the venerable vacuum AI is one smart dependable instrument. Some brands might not make the grade, I tend to ignore them as my flights are meant to be flown with the highest confidence in the equipment. Bottom line, you get what you pay for.
How dependable can be a good AI? Well, I got a chance to meet Murphy from that law department of aviation. I met him favourably way last month as I am in the final preparation for the North Atlantic crossing planned in June aboard the PA-30. One would certainly hope that all equipment, avionics and mechanical components function as they should for the 20 hours of Canadian Arctic and oceanic flying involved.
On an initial 2 hours flight to break in the right engine fresh out of overhaul, the two vacuum gyros decide to pack it in. VFR conditions no problem. First taught was that a mere 50 nm from base was far better than the occurrence at the critical point IMC between Kulusuk (BGKK) and Reykjavik (BIRK).
We tried to figure this one out in flight. Two instruments malfunctioning simultaneously… It had to be something within the vacuum tubing, right? The two vacuum pumps showing no « red witness red plugs ». The vacuum showing on the low side of 4,5 ‘’Hg. Piper requires 4,8 to 5,2. The system usually always indicated at least 5,0.
The snag had to be a leak somewhere common to the two gyros. All filters in the system were new and clean. The horizon and DG eventually came back to life but the vacuum not at all. Further troubleshooting on the ground led to speculate that the horizon might be the culprit, leaking air somewhere within. Perhaps the stabilizing vanes were seized open in there but the toppling eventually came back to some form of normality.
Enough said, the horizon was pulled out and replaced by a loaner. The vacuum came back to its normal self and both gyros started spinning happily. So heading direct to the overhaul shop I went, with the precious instrument.
It turned out that there was a crack within the filter assembly that formed and allowed the anticipated leak for one thing. The other were worn and dirty bearings that could not afford the required free spinning they are expected to provide.
Every dependable piece of equipment requires attention sometime or another. Fathom this: the horizon on this PA-30 was installed in 1994, has never been removed and flew over 1600 hours privately!
Try to get a tenth of that kind of service out of a smartphone! Granted the aircraft was always hangared and was not exposed to saline air near oceans. No aerobatics were ever performed other than my landings, its a Twin Comanche after all !