Friday, May 2, 2014
Know Your (Legal) Limits, Part 2: LA County Fire
As LA County Fire transitioned into its first two standard model 412s, we suffered from a series of issues with the Sperry automatic flight control system (AFCS). Sperry had been brought out, teeth had been ground, swear words had been used, but the answer to why the aircraft would occasionally get uncommanded tail rotor inputs was only partially understood. We were working through this problem. Unfortunately, the occurrence was rare enough that diagnosing the problem was very difficult.
One fine day I was dispatched to an accident on the 605 freeway when I pulled to a high hover to turn 180 degrees and depart the scene. The helicopter went into a soft side to side motion for about five seconds, which subsided by itself. About 10 seconds later it did the same thing again a little harder, so I parked. Long story short, this resulted in shutting down all but one lane for two hours. Lots of people going by, rolling down their windows and proclaiming what wonderful sunny beaches we enjoy in Southern California made it less than entertaining. A maintenance team came out and after an extensive examination of the aircraft, it was cleared to return to base. A week or so later FAA informed us that the crew had released the aircraft without the appropriate Maintenance Manual.
A couple of years later, I was flying one of our two standard Bell 412s FDH (fat dumb and happy) at 1,000 feet AGL, going 120 knots, when the aircraft had a significant yaw excursion to the left followed by the nose rapidly swinging to the right. The immediate corrective action was to disengage Helipilot #1, which controls the yaw axis. “Disengaging” is a polite way of saying I hit the switch with about eight times more force than necessary. The yaw quit and flight returned to normal. Shortly thereafter, dispatch called and directed us to a hoist rescue about two miles away. The paramedic up front, Bill Monahan, acknowledged the call and we were on scene almost immediately. The crew and I examined the situation and determined that a hoist was absolutely the only way to get the patient out. Even with a hoist, we would still be required to descend a couple hundred feet below the rim of a narrow canyon to get the job done. So now I have Helipilot #1 off which degrades the yaw handling qualities a bit. The mission is still doable but not optimal. We will be very close to the sides of the canyon when in position, so what happens if we do get a yaw kick? Hoist rescues are desirable by the crews of LA County Fire, who consider hoists to be a good test of their proficiency, and well-accomplished hoist missions are a thing of beauty to be admired. With this background and a very competent crew on board, I knew they would be disappointed if I canceled our involvement by requesting a second crew to be dispatched to execute the mission. But the safety culture I was in and my previous teachings on this subject told me it was the appropriate action to take. Bill ordered up a second crew and we proceeded to base. Upon arriving, Bill jumped out and did a walk around on the aircraft. This was not policy – the post-flight was up to the pilot – but I was still in the pilot’s seat finishing my paperwork. Bill asked me to come to the rear of the helicopter, where he showed me oil running off the tailboom at the 42-degree gearbox location. I quickly realized that the chip plug detector was missing from the gearbox and that no oil showed in the sight window. The 42-degree gearbox was removed by maintenance and I saw the box. Metal had begun to transfer from gear surface to gear surface, and complete failure was inevitable. How did the plug come to be missing? Good question, as the mechanic had completed his daily and I had performed my preflight check that morning, so there is good reason to think the plug was in at that time. We, the crew, had washed the aircraft that morning after the inspections. Could we have loosened the plug out of its detent? Who knows. One thing I did learn was that although these plugs are dry break when static, if the plug is missing and the gearbox is running, it will force the oil out of the box.
Bill Monahan didn’t need to do his post flight. He could have said “it’s not my job” or “it’s above my pay grade,” and maybe I get distracted by who knows what and don’t do a post flight and Bill, the other paramedic on board and myself leave widows and orphans. Thanks again Bill.
Related: Public Service News