You Are What You Eat.
Operations proceeded uneventfully enough at LZ Phoenix. The landing zone was named after a recommissioned squadron's call sign. We were training on the external transport of cargo, using the helicopter's single-point cargo hook. The student pilot hovered over the load for his third lift. The load was a metal I-beam that weighed 8,000 pounds. The student was enthusiastic, and it was his job to overcome the devious metal I-beam.
On the first lift, the I-beam, though still on the deck, had kept moving below the helicopter, jinking to the left and right, forward and back. Understandably, the student had to constantly shift his hover in a near-futile effort to stay immediately above the load. By the third lift, the I-beam was considerably more stable, because the student was doing a good job controlling the aircraft.
So here we were, hovering at about 10 feet. The four-man ground crew had just attached the straps on the I-beam to the helo's single-point, external-cargo pendant. We started to climb straight up to put tension on the load. The ground crew would stay beneath the aircraft at this time, ensuring the rigging didn't get tangled. Then we would ensure that they cleared out from the area before we actually lifted the load off the deck. I, for one, wouldn't want to stand next to 8,000 pounds of building material as it swung through the air.
As we increased power and started to climb to a higher hover, a loud bang came from the cabin. It had to have been loud because we heard it. Softer sounds, like those heard at a rock concert, are barely audible over the helicopter's freight-train roar. The jaygee student froze the controls as I called over the ICS, "What was that?"
My first thought was that something was wrong with the rigging--maybe a strap had frayed and snapped. But I was looking at the load in my mirror, and everything looked fine. (MH-53 Es have adjustable mirrors on appendages off the nose of the aircraft, like catfish whiskers. Designed for monitoring minesweeping equipment, they're also useful for external operations.) My second thought was that a window or door had slammed shut.
After a few seconds of silence, my concern grew, and I took the controls. Although the student was flying well, this was his first time doing such an operation in this aircraft, and there wasn't much room for error. Remember that we still had the load attached, and there were still four people under us. Inadvertently lifting the I-beam or letting the aircraft settle to the ground wouldn't be good.
No sooner had I taken the controls than the aerial observer, an experienced crew chief, noticed the No. 2 engine's fuel-flow gauge read zero. He immediately called, "Number two engine."
Hearing this, I immediately looked at the torque gauge and saw that the engine wasn't producing power. Loud bang plus no torque equaled compressor stall. To confirm the theory, I glanced at the T5 gauge and noticed the needle rising like a second hand going through 9 o'clock-an overtemp condition and typical symptom of a compressor stall. Fortunately, the remaining two engines easily produced enough power without allowing any settling or perceptible droop in rotor speed.
All of this happened within 10 seconds, and I pickled the load. Once again, the mirror proved valuable as I could see that the load was completely released without having to get confirmation from a crewman. I then said over the ICS that we had a No. 2 engine compressor stall and were going to land.
As briefed with the ground crew for an emergency in a hover, we slid forward and to the left before landing. Ordinarily, I would wait the few extra seconds until landing before doing any other emergency procedures, but a compressor stall, especially with the No. 2 engine, presents a high probability of an ensuing engine-compartment fire. Consequently, I told the copilot to secure the No. 2 engine. He quickly put his hand on the No. 2 engine speed-control lever, getting confirmation from me that this was the correct engine, and secured the engine. The crew cleared us below, and we landed softly in the grass.
Still concerned about a possible fire, I asked, "Anybody see any smoke or anything around the engine."
A crewman responded, "I think we got some smoke around the number two."
The student prepared to blow the fire bottle, and he put his hand on the No. 2 engine fire T-handle. Pulling the T-handle, located on the cockpit overhead, and pressing another switch would discharge a tire-extinguishing agent into the engine compartment. I then asked the crew about the status of the fire, to which the crew chief responded, "Don't think we got a fire back here. Don't see any more smoke."
With that bit of good news, we did not use the fire bottle but did expeditiously secure the engines and rotor. Postflight inspection revealed there had been a flash fire in the engine compartment. It would have gotten quite a bit worse if we had let the engine run much longer.
Further inspection (this time by QA reps) revealed the probable cause of the compressor stall. At the intake of each engine, the MH-53E has something called an engine air-particle separator (EAPS). It's a simple device designed to prevent the engine from ingesting FOD, such as bolts, rivets and washers. Ironically, in this case, a rivet from the EAPS had probably caused the compressor stall. We had preflighted the engine intake and EAPS barrel. Upon postflight, QA found a. missing rivet at the front of the EAPS.
As a result of this potential mishap, squadron pilots and aircrew are paying closer attention to the EAPS barrels during preflight. The squadron has people who specifically examine the EAPS as part of daily inspections. Furthermore, a minor design modification of the EAPS was already in work at the time of the incident, and all squadron aircraft have incorporated this airframe change.
I should have noted the power the engines had produced on previous flights and returned to base if the weak No. 2 engine was a new abnormality. Good aircrew coordination prevented further problems, but even here, it's debatable whether I should have taken the controls after the compressor stall. In retrospect, I think that the transfer of control added an unnecessary complication, and it would have been easier to diagnose the problem and do the appropriate emergency procedures while not having to worry about maintaining a stable hover. We were fortunate to have not learned these lessons at a much higher price.
Lt. Gallo flies with HMT-302.
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|Date:||Apr 1, 2000|
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