|The airplane and the landing gear wanted to go different directions.|
The C-5 Galaxy is a magnificent airplane. I flew this amazing machine for over a decade and many thousands of hours between the years of 1991 and 2003 while a member of the 312th Airlift Squadron at Travis AFB near San Francisco. And while the airplane has some amazing capabilities, she would occasionally break in really creative ways. What follows is the story of one of those times.
The grandiosity of this airplane is difficult to convey in both word and picture; she must be seen in person to be fully believed. I still recall my first flight aboard a C-5 as a student at Altus AFB. It was difficult to get my head around the thought that the thing actually moved when we taxied out of parking, let alone flew. And yet fly she did.
She was a pleasure to fly. One of the design engineers at Lockheed must have at some point taken his father's Cadillac Brougham out for a joyride because that is an apt description of her ride. She was big, but with full time three axis flight augmentation, she was lighter on the controls than a 737. She was equally agile on the ground with the ability to execute a 180 degree turn on a 150 foot wide runway (using 147 feet, according to the flight manual). This fun fact ties in to our story.
The Elegance of Simplicity Never Applied to the C-5
The size of this aircraft presented many new and unique challenges to her builders, the Lockheed Corporation. As an aside, the Boeing Corporation, losers of the original competition to build the CX-HLS heavy lifter back in the sixties, went on to use the resources gathered for that project to build the 747. Lockheed, the winner of the contract, was faced with the problem of creating a drive on drive off airlifter with a footprint capable of operations on soft field forward operating locations.
The solution was to employ four main landing gear accommodating six tires each for a total of 24 main landing gear tires. A four tire nose gear brought the total to 28. Spreading the maximum 840,000 lb. weight of the aircraft over 28 tires was expected to allow operations on fields having less weight bearing capacity or thinner pavement. It wouldn't break up the concrete or sink into the mud. C-5s even land on ice in Antarctica due to this soft footprint.
The four landing gear however, arranged in a tandem, or two by two, presented another problem: turning. Getting the airplane turned around in as short a radius as possible meant that the gear would scrub furiously in the turn. Anyone who's ever pulled a tandem wheel trailer around a tight corner has experienced this. The solution is the same as that used on those large carts at your local big box store. Just make the rear wheels caster or turn.
So that is how the airplane was designed. When going into a turn, the pilot in the left seat would throw a switch on the center console which released hydraulic pressure from the rear main gear allowing them to caster like a shopping cart wheel. When steering out of a turn, he or she would then return the switch which would apply pressure to drive the gear back into alignment. The copilot was charged with keeping an eye on gauges indicating the caster angle to ensure the gear were powering back to their aligned position when coming out of the turn. Rube Goldberg would have been proud.
The Ghost in This Machine is Named Murphy
The date was July 8, 1999 and the place was Kadena Air Base, Okinawa, Japan. We were on a WestPac "channel" mission. That meant a routine five or six day jaunt around the Pacific Rim moving opportunistic cargo and household baggage from reassigned military families. The purpose of this type of mission was ostensibly for training, so what was carried was not of real import. Many times, in fact, there might be a FedEx or UPS plane shadowing our route carrying stuff that was actually important. The C-5 was voluminous, but alas not too reliable as we shall see.
Though I don't recall exact numbers, we probably had a cabin load of perhaps 150,000 lbs. and a fuel load of perhaps 225,000 lbs. for a takeoff gross weight of about 750,000 lbs. Our destination was Elmendorf AFB in Anchorage, Alaska, a distance of 4400 miles, so we were somewhat heavy. It was an entirely routine mission planned for perhaps eight or nine hours depending on the winds.
I was in the jump seat for takeoff as we were an augmented crew with three pilots. Being augmented meant that our crew duty day could be stretched to 24 hours if need be. Engine start was normal as was taxi out of parking down the parallel taxiway. It was on the turn from the parallel taxiway and onto the hammerhead that we encountered a bit of bother.
As per normal, when the pilot started the turn, he reached over and flipped the red guarded caster power-back switch to the caster position and stated "caster" on the interphone. And as we came out of the turn, the pilot returned the switch to its original position which should have driven the gear back into alignment.
This didn't happen. Coming out of the turn, the airplane chugged a little bit and came to a halt. What this normally meant was that one of the gear lagged a bit while powering back to the center position. And sure enough, that is what the right rear gear indicator showed. It was out of alignment by perhaps 20 degrees.
This meant that the gear did not automatically return to alignment. The approved fix was to roll the airplane forward a bit while the copilot manually commanded the gear to center using the manual power-back switches. The airplane had to be moving for this to work. So that's what we did...or tried to do.
At first the airplane wouldn't move, so the only solution which presented itself was to add more power. A lot more power. The pilot pushed up the throttles further and eventually the airplane did move, but not willingly. She was bucking like a bronco and the errant gear was still not moving to center.
After about as much of this as we could stand, we stopped the airplane and deplaned one of our engineers to take a look. What we heard next on the interphone told us that something was amiss. "Holy $#!%...You have GOT to see this!!" or something to that effect. It was at this point that we realized that we were probably not going to go flying that day.
How Did It Get Like That?
The engines were shut down, maintenance was called, and I climbed down the two stories from the cockpit to take a look myself. What I saw amazed me and reinforced my belief that Lockheed built one tough airplane.
The reason the airplane didn't want to roll was not because the gear had failed to return to center. It had. But it hadn't stopped at the center position. A failure of the caster power-back valve allowed the gear to not only center from the left but to keep on going in the opposite direction to the right. The airplane was trying to roll straight ahead but the right rear gear wanted to go right and was being drug. There were thick black rubber marks trailing behind as it was drug at a sideways angle while supporting over 100,000 lbs. of weight.
But the most remarkable sight was that of the gear strut. This piece of metal which supports the six tire gear truck is perhaps several feet in diameter, and it was bent at a very unmistakable angle away from its partner on the front gear. I was amazed that the supporting structure had even held together as it must have been under thousands of pounds of sideways pressure. It seemed a sure bet that some sort of internal damage must have occurred.
Well, the maintenance guys disagreed. Apparently this was no big deal, at least from a structural point of view. The fix was even easier. The C-5 has the capability to "kneel" down which means it can be lowered on its struts so vehicles can drive on and off. What is even more convenient is that each individual gear truck can be "kneeled" by itself meaning that it will lift off the ground while the other three main gear support the aircraft. Very handy for tire changes.
So the maintenance guys merely kneeled the errant gear as the entire airplane creaked and groaned while coming back into alignment. The bad valve was replaced, and the next day we were on our way back home with the added bonus of an extra day on beautiful tropical Okinawa, and an extra day of per diem to boot!
|The author in front of the stricken plane.|