From a comment on Flight Global -
There are times when I think Fly-By-Wire (FBW) enthusiasm is getting out of hand. Some reasons for my concerns:
About 1982 a prototype SH60B Seahawk was performing an automatic approach to hover over the deck of a frigate when the ship turned on its radar. The Automatic Flight Control System (AFCS) went badly wrong, forcing the pilot to shut the system down and take manual control to save the aircraft.
Also in the 1980s a Black Hawk helicopter flying by a 50,000 watt commercial radio tower crashed when the movable horizontal stabilator (the only FBW control on the aircraft, was driven to the full down position forcing the helicopter into an uncontrolled dive. The crew died.
After both these incidents the aircraft systems were successfully hardened to prevent the reoccurrence of the incident. Now for the a present example of concern;
In an military technology magazine in the 1990s was an article on future energy weapons in which was described an incident where an AGISS cruiser locked onto a passing F-16 with a focused beam from its SPY-1 radar (a Phased Array type radar). The F-16 lost control to such an extent, that the pilot declared an emergency and only regained control when the radar operator turned off the radar. The article goes on to note the Navy was continuing studies into the affect of the focused radar beam on FBW systems.
Putting these examples together with the ban on using cell phones and other electronic equipment by passengers in commercial airliners one has to come to the conclusion that outside electronic interference and FBW may not mix very well.
I have worked in the helicopter industry for the past few decades, and I have begun to be concerned about this push to FBW in combat helicopters. It seems to me to be a Let’s-Get-On-The-Bandwagon philosophy, driven by generals and engineers with very little thought about the ramifications on the pilot and crew who will fly in harms way.
Basically flying a helicopter is vintage World War One flying, low altitude and low speed, with no parachute. Besides that helicopters have proven extremely bad at gliding. They autorotate down, this requires a definite control input, which would be lacking in a fried FBW system. Current combat helicopters have redundant control runs and multiple load path linkages, mechanical systems, which are augmented by AFCS to ease pilot work load and the controls have mostly benign failure modes. The benign modes are because a hundred years of aviation trial and error have made mechanical flight controls (MFC) harder to damage and to fail catastrophically (though, of course, it can happen).
Now there are good points to FBW, such control improvements reduce pilot work loads, however modern AFCS do the same. As observed by comparison of the UH60L with the new UH60M, the “M” is much easier to fly than the “L”. The “M” AFCS is 21st century, as compared to the 1980s technology of the “L”, with loads of workload reducing options. Come to think of it, the AFCS computer on board the UH60M is based on FBW without the wire control runs. If this is so with the US Army’s newest combat aircraft, what then is the performance improvement that justifies the costs and risks of adding a FBW system to a helicopter, especially when the result of FBW failure is death.
If the AFCS (the computer gets fried) goes down on the UH60M, the pilot can still fly manually. If he had to, he could even complete his mission. The engines though installed with electronic fuel control still have a redundant mechanical backup. All this designed in redundancy is based on the combat short comings of the Huey in Vietnam.
What I am afraid of is there will come a time when anyone with a powerfull radar and ultimately a designed for purpose energy weapon will start disabling or destroying FBW systems and especially with Helicopters there will be no recovery and no bail out, because the new whizz-bang technology won out to common sense.
Combat Helicopters and Fly-By-Wire - Defence - Defence - Aviation Forums - Flightglobal Airspace