Bizzare accident onboard Truman

reply to post by Zaphod58


Usually EMI is more likely to interfere with more delicate electronic systems like flight control computers and digital instruments, highly unlikely the circuit of a powered down aircraft could be affected. Military systems are usually tested and shielded for EMI, but it is still possible. Interesting only one wing moved not both. You're right probably mechanical issue.

reply to post by JimTSpock


I'm leaning that way, but figured this would be an interesting discussion, with the coincidence of them testing the UCAV on board, and this being one of the first times I've heard of this type of accident. I know they've happened before, but the timing of this is very interesting.

Just a semi-educated (OK, illiterate!) guess on my part, but it seems to me that the hydraulic system on a Hawkeye had to have been perfected early on in its lifecycle, like fifty years ago. The mechanism must be a basic electrical signal activating hydraulics--nothing really electronically fancy (Think of the systems on cars built in the sixties.) Although the radar electronics and ECM stuff must have been revised a zillion times since their first deployments, it would seem unlikely that the wing deployment hydraulics would have been extensively revised. I admit to having seen Navy tech manuals that are Rev 20, Change 54 (always when we needed Change 55), but still, I'm having a hard time envisioning a rev that would subject it to advanced EMI. Wish we had a Hawkeye tech on board to advise.

reply to post by schuyler


I'm not a Hawkeye person, but I've seen where a spurious EMI signal to another part of the plane, has led to a subsystem activating, or even a system not even connected to where the EMI signal hit.

That being said, I think the odds are that a hydraulic pump failed, releasing pressure to the mechanism. Like I said, I just find this a really odd coincidence, that the X-47 happened to be there when this happened.

The Hawkeye itself emits a shedload of EMI - that dish on top has a peak output of 1 MW........one would think that any vulnerability to that might be knwn already!!

As for it's hydraulics being fully developed - maybe - but every seal gets replaced, every actuator overhauled - there are many ways a defect can be introduced into a full developed system

Originally posted by Aloysius the Gaul
The Hawkeye itself emits a shedload of EMI - that dish on top has a peak output of 1 MW........one would think that any vulnerability to that might be knwn already!!

As for it's hydraulics being fully developed - maybe - but every seal gets replaced, every actuator overhauled - there are many ways a defect can be introduced into a full developed system

Sure (and I think we agree), but a seal is not subject to EMI and an actuator is still blunt-force started by a solenoid and a dose of battery-induced electricity just like a automotive starter engine. Not much to it, technically speaking. My conjecture here (and admittedly only conjecture) is that a "mature" system designed in the fifties is a) unlikely to be affected by high frequency EMI and b) unlikely to have been modified to the point that it is.

Obviously something broke, and if it were ever overhauled during its lifetime we can blame the mod. All I'm saying is that I don't think we can hang our hat on EMI here. Maybe, but other than proximity and the uniqueness of its presence we don't have any evidence the 47B is at fault.

Originally posted by schuyler----->Obviously something broke

Or somebody forgot the lock pin

I personally don't know the details of the aircraft, but could be a lot a little stupid things. Something like a mechanical switch being out of position might have an indicator show the wing was moved to the full lock position when it wasn't. Or it could be something like catch wearing down or not being greased properly and failing to lock when it's presumed that it did. Or maybe some guy responsible for putting a lock pin somewhere didn't shove the dang thing all the way in even though he pushed and jammed at it as hard as he could, as some things can be a real PITA that way, and ended up running to some other task because some chief was riding on his...

Some spurious signal from an EM source would seem lower on the checklist of things to go wrong. (Particularly on older aircraft where it's unlikely a computer is controlling something.) I'm sure whoever is responsible is going over the logs, etc.

My guess is that they forgot to chain one of the wings after they were folded. Then the hydraulic cylinder lost pressure, allowing the wing to swing forward.

reply to post by allenidaho


Most likely. Like I said, I just found it really interesting that the X-47, which was tested to a much higher standard in the anechoic chamber was on board at the time of the accident. I don't think the aircraft itself would have much in the way of spurious signals that could cause this to happen, but the arm controller is another story.