Eielson Air Force Base F-35 crash

Craig said:
It appears that the hydraulic system was hand serviced and the source of the fluid in the hand cart was from a drum that was found to be 40% water.... Another article stated that several days prior, another aircraft had a similar issue, but did not do a touch and go, and turned it into a full stop landing. Hydraulics were also found to be heavily contaminated with water.

Fly by wire aircraft undergo a control gains change when the weight on wheels switches make or break contact. In this case, they didn't break contact after the second takeoff.
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When I was active USAF, I got to spend an evening helping flush and reservice several F-15 AMADs and IDGs (gearboxes and generators) because a young airman serviced an oil cart with Citri-Clean rather than the 7808 that was required. The maintenance sucked but at least everything smelled wonderful. It was just pure luck that no one serviced an engine that evening.

That was a mistake of choosing the wrong barrel though. This sounds like the barrel of hyd fluid was contaminated with water, a lot of water. I wonder if it got contaminated while in the servicing area, or if it was received already contaminated. And how did it go that long and apparently wasn’t discovered until the investigation?

Just to note, the article said they discovered the water in the nose and right main landing gear. That would infer that the contamination was in the struts and not the main hyd systems…could be both I guess? Ice in the struts would certainly contribute to the landing gear not extending; ice in the main hyd systems, not so much. That said, on most of the 35 flight lines I’ve been on, servicing of the main hyd system from a hand cart does occasionally occur, but not often. The main reservoirs are usually serviced with the powered hyd cart, and those carts are filled by a different squadron (EMS). Meaning that the powered hyd carts and smaller hand hyd carts are serviced by two different units, thus two different barrels/fluid sources.
 
After reading other articles posted about the crash, some of my own questions have been answered…

Agree with @Craig some heads are gonna roll over that one. That sucks.

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Craig said:
It appears that the hydraulic system was hand serviced and the source of the fluid in the hand cart was from a drum that was found to be 40% water.... Another article stated that several days prior, another aircraft had a similar issue, but did not do a touch and go, and turned it into a full stop landing. Hydraulics were also found to be heavily contaminated with water.

Fly by wire aircraft undergo a control gains change when the weight on wheels switches make or break contact. In this case, they didn't break contact after the second takeoff.
Click to expand...
Not all of them. Some have much better logic to back up the switches, and make sure the aircraft is really not flying anymore.
 
keen9 said:
Not all of them. Some have much better logic to back up the switches, and make sure the aircraft is really not flying anymore.
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All I can tell you is that everything I work on with fly-by-wire has huge warnings in the maintenance manuals, that batteries must be disconnected when jacking the aircraft. Applying ground power while on jacks, without the WoW switches held in the ground position or bypassed to the ground position will cause the aircraft to instantly go into flight mode and the emergency power system will activate and flight controls will start moving.
 
Craig said:
All I can tell you is that everything I work on with fly-by-wire has huge warnings in the maintenance manuals, that batteries must be disconnected when jacking the aircraft. Applying ground power while on jacks, without the WoW switches held in the ground position or bypassed to the ground position will cause the aircraft to instantly go into flight mode and the emergency power system will activate and flight controls will start moving.
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Right, but I'm talking about transition from flight to ground. A good design puts the controls in flight mode for most odd cases because as seen in this incident, you really don't want to be in ground mode when you are flying. That is why in maintenance, you want to be sure WOW is on ground (also that airspeed is zero, but it is usually only testers, not maintainers that get to do that).
 
Craig said:
Someone's going to lose their job and maybe some rank over this one...Letting barrels of hydraulic fluid get contaminated with that much water and them getting to the point of use.
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Yep. In my Naval Air Safety Officer days this would have come down as maintenance malpractice.
 
keen9 said:
Right, but I'm talking about transition from flight to ground. A good design puts the controls in flight mode for most odd cases
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Another example of A/G logic going wrong:

The Sikorsky S-97 Raider prototype destroyed by a hard landing in 2017 suffered extreme roll oscillations as the aircraft’s flight control software transitioned from ground to air modes during takeoff, according to the National Transportation Safety Board’s (NTSB’s) newly-released factual report.
The left to right rolls were so severe that the counter-rotating coaxial blades intermeshed and hit each other, “creating a cloud of blade fragments and gray dust,” according to the NTSB’s Helicopter Specialist Report, published April 30.

The NTSB’s report notes that the Raider has three flight control modes, referred to as paths: a fully-on-ground path, a fully-in-air path, and a transition path. If any one of the aircraft’s three wheels are on the ground, the on-ground path is engaged. If all three wheels are off the ground for more than three seconds, the helicopter switches to the fully-in-air path. The two are blended during the transition from air to ground, or ground to air. During the three seconds after the last wheel touches off from the ground, or 0.5 seconds after a wheel touches the ground, the flight controls are in the in-transition path.

The report notes that control law changes were introduced by Sikorsky in late 2015 to improve ground to air transitions.

“An unintended by-product of these changes was an increase of the cyclic stick sensitivity by 2.5 times while operating in the in-transition path,” the report notes.

During the timeline of events in the hard landing, the report states that the left main landing gear briefly contacted the ground during one of the rolls, resetting the transition to flight mode.

verticalmag.com

NTSB releases more details on S-97 Raider accident

The Sikorsky S-97 Raider prototype destroyed during flight testing in 2017 experienced a catastrophic intermeshing of its coaxial main rotor blades, the National Transportation Safety Board revealed.
verticalmag.com verticalmag.com
 
keen9 said:
Right, but I'm talking about transition from flight to ground. A good design puts the controls in flight mode for most odd cases because as seen in this incident, you really don't want to be in ground mode when you are flying. That is why in maintenance, you want to be sure WOW is on ground (also that airspeed is zero, but it is usually only testers, not maintainers that get to do that).
Click to expand...
As a maintainer, there are quite a few test sequences where we have to have the jet "think" it's flying. The critical thing, is setting it up and making sure all the safeguards are in place to prevent it "thinking" that flight controls should be active as well.
 
I will be at Eielison today…I have a son in law that flys F-35’s and I’m visiting my granddogs. I will be happy to take your questions and comments directly to the Commissary manager and report back. Just my take but seems like this issue has been fixed…I came from a strong MTP background from the Army and asked some questions just because it was personal…
 
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