Hot Air

Sometimes the answer really is crazy

The air crew came back from a sortie reporting that the air conditioning system went full hot during the flight and required the ram air override.

I ran the night shift in our shop and was also the QA for all maintenance. I knew this aircraft well.

The plane was ‘fixed’ 2 times prior and now the Chief had ‘downed’ the airplane. 114 was moved to the hangar deck and buried deep. Over the next 2 weeks, we went over every possible item in the system. However, we were thwarted a bit in our troubleshooting because this type of problem really needed to have the engine running for proper evaluation. Of course, that was not an option in the hangar deck. The second best method was to connect a ‘huffer’ to the airplane and run the system off of that. This is the equipment that starts jets. We were still at a disadvantage because the jet was buried so deeply in the hanger bay that we could not get a huffer on it. When we did have a chance, it was only for a very short time frame.

During those occasional tests with the huffer, I noticed that the pneumatic system pressure was running on the lower end of the acceptable range. However, the system checked out in every respect. Valves worked properly, the system cooled and we checked every piece of ducting and servo air piping for cracks and leaks and found nothing. There were hundreds of items that ran off of this system and we couldn’t find any problems.

We went to several other aircraft to measure the real world pressures and behavior to help us determine whether these pressures were normal and we found that each airplane ran pressures in the range but at a different ‘normal’. We also found that different huffers produced different results, adding to the confusion.

Two weeks of downtime was enough for the Chief. One night at our maintenance meeting, I was given an ultimatum. “Wiker, you better fix 114 or I am gonna have your ass!”

The Chief was tough but fair. I retorted, “Chief, in that case, I need your help.” He quickly responded to my 2 requests. Put the aircraft near the hanger bay door and get me a huffer on standby ALL NIGHT! Chief was good. He knew that if he removed my excuses, I would have no other choice but to perform. “Consider it done.”

The hangar deck had been resorted within the hour and my huffer was standing by. We got on the airplane and tested everything from stem to stern. The bleed air system, the cooling system, pressure regulators, valves, tubing, connectors….. There were gauges hanging on every port.

I was sitting in the cockpit. Cold air was coming from the system but I knew that once the airplane took off again, the problem would return. There HAD to be something wrong. I turned around in the seat, kneeling in the cockpit and testing the G-suit valves. Everything was fine. Then, just for grins, I disconnected the seat cushions and used whatever I could find to plug the hoses.

I heard a holler from the deck that the pressures had risen 2 1/2 psi! I had one of my airmen watch the gauges while I plugged in each of the seat cushions. “Two tenths” he hollered each time I connected another cushion. “One point eight” he yelled when I connected one more. I disconnected the cushion and threw it to the airman. “Get up to PR and get me another cushion”. He scurried away to return with a new one. I plugged in the new cushion and the familiar “two tenths” is what I heard.

I turned in my MAF (Maintenance Action Form) to the Chief. He noted immediately that the aircraft listed was 114. He read through all of our notes. Pressures, troubleshooting procedures...then he saw the corrective action. “R&R rear seat cushion”. There was a flurry of expletives, brow beating and disgust poured out on me over the next few minutes. I just responded, “Chief, that was the problem and I am not changing that MAF.” I knew I was going to be sent on temporary duty to the worst place on the ship if I was wrong. I had run out of other ‘reasons’ and decided that if I was wrong, I would realize that I was as stupid as he indicated that I was.

114 flew the next day and we stood by for the flight crew’s return. “It was fine” was the extent of our feedback. The whole shop was floored. A seat cushion grounded a $30 million aircraft. The only explanation that I could come up with is that at altitude, the cushion would ‘leak’ more than at sea level due to the pressure differential. This differential caused enough flow from the system to cause it to fall out of the acceptable range and thereby causing dependent valves to become inoperative.

I didn’t care. I was not washing pots in the galley.