Stuck throttle trigger partly to blame in Thunderbirds crash

The AIB report on the Thunderbirds Solo F-16 crash in Colorado Springs has determined that a stuck throttle trigger was partly to blame.

Major Alex Turner was flying Thunderbird #6 as part of a six ship formation that had just performed a flyover of the Air Force Academy graduation ceremony. The flight had returned to Buckley AFB and was beginning landing procedures, when Major Turner reported an engine failure. He guided the aircraft to an empty field before ejecting.

The AIB found that during his landing attempt, Maj. Turner made an inadvertent throttle movement, pulling the throttle to cutoff. Under normal conditions it wouldn't be possible to pull the throttle back to that position without activating the trigger switch. When the AIB examined the throttle, they found debris around the switch, and that it was stuck in the engaged position, allowing the throttle to be pulled to the cutoff position. Major Turner was too low to restart the engine at the time.

www.acc.af.mil...

a reply to: Zaphod58
Interesting. So maybe he was just trying to reduce the throttle, and was counting on the built in protection to prevent the throttle from going to zero, but since that protection was gone due to the stuck switch it ended up going to zero?

I don't understand how that's inadvertent. It seems like even if the protection had been in place if the switch wasn't stuck, he still shouldn't be attempting to test that by attempting to reduce the throttle to zero, should he?

Thunderbird's are my favorite, I grew up right next to General Dynamics airstrip. I've seen and talked to some of the best pilots in the world. The stunts these guys pull can wear out any part of the aircraft real fast.... who would of thunk wear on the trigger assembly.

a reply to: Arbitrageur

More like he reduced throttle to the proper setting, and as he moved to look out at something, or shifted in the seat his hand moved without meaning to, and since the switch was stuck it killed the throttle.

I had to look up the throttle to understand how it rotates. Basically, all fighter type jets will have an idle stop, so you can effectively jam the throttle back to idle and it will stop. Most have some sort of mechanism to further retard the throttle to sub-idle or off. The Tomcat, for instance, had to have the throttles move outboard, one engine at a time, in order to shut off the motors. IIRC, the T-45 Goshawk was similar. Move throttle aft until it stops (at idle), then push it outboard and then backwards to shut off.

Sounds like the F-16 has a pinky switch that allows the throttle to rotate, then move aft to the off position. If the pinky switch is stuck, then the throttle could rotate at any time, allowing the throttle to be moved further back than it should go, which would shut down the motor. Depending upon altitude and airspeed, you may not have enough time for a relight, once you discover that your engine is no worky.

Glad he made it out OK. It's a bad finding to discover FOD in the switch. I would expect a potential redesign of the switch or the mechanism, along with increased vigilance on FOD.

a reply to: cosmania

I'm actually surprised to hear there was FOD in the switch. Even if it was just dirt build up, I'd think that would be something they'd inspect at least often enough to catch it before the switch gets stuck.

a reply to: Zaphod58

You can see the throttle in the vid. How does it twist Zaphod?

a reply to: GuidedKill

It's not a twist, it's just a straightforward forward and back. Rotation isn't really the best word for it, but it's technically correct. The throttle is on a curved track so it goes up and back down at either end. One end is cutoff, the other is, in this case, afterburner.

Could they just fit a new type of button that lights up when its pressed? the pilot would of known probably on take off that the planes switch would of been faulty and got another one to fly in? Total cost probably a few hundred bucks per plane which is a lot cheaper than having to replace an f16 i'd bet.

First I'd want to know if checking the throttle switch for correct operation is part of a time or phase inspection? If it was then I'd be looking at the person who performed that inspection and check if they know how to do it correctly. I would also look at who the Quality Assurance person who signed off on the inspection. If it is not, then I'd look at adding it to one of the inspections. Right now, I'd have every F-16 inspected to assure that the switch operated correctly.

a reply to: GuidedKill

Never mind the throttle in that video, pay attention to how dirty that console is... there is enough gritty, sandy debris in there. They need an onboard vacuum system or a power washer

originally posted by: Maxatoria
Could they just fit a new type of button that lights up when its pressed? the pilot would of known probably on take off that the planes switch would of been faulty and got another one to fly in? Total cost probably a few hundred bucks per plane which is a lot cheaper than having to replace an f16 i'd bet.

It may not be an electrical switch to begin with. It could be a mechanical lockout like most cars have on their shifter to go from one position to the next.
In that case, adding an electrical switch to detect the lockout position might actually mean finding a means of adding a wire to the mechanism, another thing that could get caught up in the works later when least expected. Then there is the whole place on the console to put the light and it is another thing the pilot will have to keep track of.

I would think proper preventative cleaning on a regular schedule should prove far more effective as well as cost less and have the planes avoid extra downtime as they would need a retrofit and probably some sort of airworthiness testing/certification.

a reply to: evc1shop

With no idea on the actual mechanics of an f-16 I was just thinking of what would be a simple idea to alert the pilot should it go wrong. Obviously proper maintenance should be of top priority but I wonder since these seem to be a demo team that perhaps they don't get the full work up that operational jets do?

a reply to: Maxatoria

They actually go through more checks than a fleet aircraft does. They put a lot more stress on the airframes than normal use. Usually when they replace the aircraft, the ones being replaced go straight to the Boneyard, because they've had so many over G flights.

a reply to: Zaphod58

I work on global express, the throttles have a button to be able to go from idle to thrust reverse deployment, this won't work in flight, the wow switches have to activate for this to happen.

The engines are turned off with a toggle switch below the throttles, this will also only work in the air if the fire T-handles are pulled first to cut off fuel, Hyds and generators.

Maintenance checked the aircraft two days prior to the crash and didn't find any problems. The switch has given other aircraft problems before. They're looking at calling for pilots to swab the area around the switch prior to taking off as an interim solution until a permanent fix can be developed.

"Here you go, Capt Smith, don't forget to swab your throttle"

That won't be an ongoing joke for those guys, or anything.

a reply to: cosmania

Pilots and ground crews never make jokes like that. They're always completely...

Nope, couldn't do it. I tried to get it out with a straight face.