Captain James T Webb -- Air Forces Iceland
Thank heaven it was a taxi accident! It was an overcast morning when the crew completed pre-flight of their EC-121, airborne warning and control aircraft. Everything checked out okay, and the 17 crew members piled into their aircraft for what was to be a routine training mission. The engines were started, and the copilot called the tower for taxi clearance. Tower cleared the aircraft to taxi and the chocks were pulled. Things were going exceptionally smooth this morning, with plenty of time to taxi, for it was 20 minutes before the scheduled 0900 takeoff time. With her full fuel load, the aircraft lumbered down the long parallel taxiway as the crew prepared for take-off, the left tip tank dug into the taxiway apron and the aircraft started to rotate rapidly to the left. The pilot quickly reversed number three and four throttles and applied right brake in an effort to stop the aircraft and prevent further rotation. Simultaneously, the copilot joined the pilot on the right brake and then tried the emergency brake system as the aircraft continued rotating 120 degrees while sliding to a stop. When the left wing fell to the ground. the right wing and wingtip fuel tank (with its 2 tons of fuel) whipped upward in a violent motion. As the aircraft rotated left, the right tip tank snapped off. ruptured, and was caught under the rear fuselage spreading a bed of fuel for the aircraft when it stopped. Fed by ruptured fuel lines. fire in the left wheel-well was already out-of-control when the aircraft came to rest.
A 23-knot wind fanned the fire from the left back toward the fuselage and the 17 souls inside. When the aircraft stopped, a total of about 8 seconds had elapsed from the initial drop.
Seeing reflection of flames off the number two engine shroud, the pilot ordered the flight engineer to cut all mixtures and rang the emergency alarm bell. The crew members in the aft cabin were already keyed for action. The rear crew door was opened, the egress rope thrown out, and they began scurrying out the door. Some used the rope and some, the more impetuous ones, elected to jump to the ground. One individual opened the left over wing hatch but was greeted with flames blocking the exit. He then opened the right over wing hatch and saw flames already coming up over the wing's leading edge. He and a close friend dashed through this exit and departed off the right wing's trailing edge. After cutting the mixtures, the flight engineer opened the forward crew exit door only to see a cloud of black smoke billowing from directly below. The pilot, copilot, and engineer noted the path to the rear exit was still clear. The pilot ordered them out via that exit. They assembled upwind and took a head count which confirmed everyone clear of the burning craft. The entire evacuation took less than 30 seconds with only two minimal injuries. One individual had his gloves off to adjust his camera when the mishap occurred and obtained rope burns on his hands when he slid down the egress rope. Another slipped while going off the right wing and bruised his leg.
The fire trucks were on the scene immediately but were unable to suppress the massive fire. The crew were examined at the hospital and released. They spent the next few hours rehashing the events during the evacuation and giving thanks and praise for the egress training they received prior to the accident. Their professional, systematic actions, and their knowledge of what to do and how to do it before the need presented itself were instrumental in their escape from an aircraft being engulfed in flames. Their training and "heads-up" thinking resulted in avoiding a near catastrophe.
Avoiding a near catastrophe? Catastrophe is similar to beauty-- it's in the eye of the beholder. And if you're the commander of a unit beholding one of your $2,500,000 air craft burning to the ground, things aren't exactly beautiful! In fact, until you find out what happened, the catastrophe may be just beginning.
But there is still "no excuse"-- so how about a reason? The gear failure was caused by a single, small nick in the surface of the landing gear's upper cylinder. The nick was only 0.6 inches long and 0.015 inches deep but the corrosion in the base metal grew until the cylinder could no longer take the stress from normal operations. The corrosive process was like a hidden time-bomb, slowly growing, slowly ticking off time, until it exploded causing catastrophic failure of the complete gear assembly.
During the accident investigation, it was determined that this nick was on the gear when installed on the aircraft just 1 month prior to the accident. Obviously, no one could have seen the corrosion under the nick, but the nick itself would have been clearly discernible by anyone inspecting the gear during overhaul, packing, un-crating, installation, and routine walk-around inspections. Yet, of all the people having "intimate relations" with this gear, no one noticed the nick until it was pointed out by a depot representative during the investigation. It then stood out like a cherry on a Las Vegas slot machine. Why?
Eyesight wasn't the problem. Everyone involved had adequate vision to read the print in the tech data and make sure there were no requirements for checking for mechanical defects on the non-chromed surfaces of the strut. The lack of tech data was part of the problem, but vision was obviously not a factor. So why wasn't the nick detected?
answer is in the understanding of the phenomenon called perception. Perception involves
not only focusing one's attention on the cue, the nick in this case. but also
attaching a degree of value to the cue to make it significant. The addition of a
specific check to the tech data should solve the problem of directing attention to such
defects. But how do you get someone to attach the appropriate, significant value? Perhaps
the question can be partially answered by reinforcing one's value system through
Fractured cylinder that finally failed from corrosion under small nick shown in left photo. Tiny nick, just .6" long and escaped observation.
The photograph left shows the nick on the gear strut. If you can imagine the cylinder all in one piece, the nick might not mean much to you--not significant. However, associate the nick with the fractured cylinder shown in the photo left. Does the nick have any significance now?If your work involves inspection of aircraft components--it should have significance! Whether you fly the birds, maintain them, or support them in any way, YOUR JOB IS VITALLY IMPORTANT. Your attention to the condition of aircraft components from landing gears to the smallest electrical diode is important. Your identification of the seemingly most insignificant defect could mean the saving of invaluable life.
That 5¢ nick could have millions of dollars worth of corrosion under it and many souls riding on it. *
Notes from Larry Franzen
The safety article did not provide the complete story on the gear maintenance. Aircraft 121 had been stored at Homestead for almost a year. Serious corrosion had taken its toll, so a depot team was called in to perform repairs. # 1 engine was removed to permit doublers to be installed on the firewall. This moved the throttle cable pulleys forward and required complete rework of the engine control cables. Fuselage skin was removed and replaced. I am not sure of the other repairs. As I recall, 2 - 3 months was required to complete the work. On the day of the first scheduled flight, the left gear was flat. A new gear was ordered and received in the evening. An overnight crew was assembled to change the gear. The aircraft was towed into an old seldom-used hangar that had very poor lighting. The maintenance crew worked with flashlights to change the gear. Under the circumstances, the nick mentioned in the article was most probably undetected. The plane departed for KEV. immediately after the gear was installed.
Photos of 55-0121 burning