Two summers ago, a British Airways crew found themselves unable to provide roll control to their Boeing 747-136 as the 28 year old aircraft carried some 300 passengers from Detroit, Mich., to London, England. The crew first became aware of the problem when the autopilot failed to alter the jet’s course, as it should have, at altitude, en-route. As the pilots made a check of their systems, they noticed something egregiously wrong. The control column, had “seized solid” during the flight, locking the ailerons at dead center. The pilots were quite literally frozen at the controls. The crew worked together to apply all their cumulative strength to the yoke and, through those efforts, were able to make only the most subtle adjustments in bank before the ailerons broke free — only to seize up again later in the flight. As the aircraft made its way across the Irish Sea, the stunned crew declared “Pan Pan Pan” for radio silence and requested priority for landing at Heathrow. The aircraft descended straight ahead until the crew finally managed to fight the controls free at approximately 11,000ft through the use of “extreme force.” The aircraft landed without incident.
A report by the Air Accidents Investigation Branch in the U.K. suggests that aside from this one incident, similar occurrences had taken place no less than 14 times on British Airways 747-136 aircraft. As it turns out, another crew had suffered a similar problem in the same aircraft just five days earlier. Why the problem had not been seriously addressed and remedied is not clear, but it is likely that rumors were spreading through the ranks of pilots and flight engineers like wildfire. The fact that these occurrences were allowed to repeat — allowed by pilots, mechanics and management — is almost surreal. However, perhaps the inaction can be attributed to the inability of anyone to reproduce the system failure on the ground. After all, you can’t fix problems that “don’t exist” and it would be foolish to ground a revenue-generating aircraft for a non-existent problem.
Fortunately, after a near emergency landing, clearly there *was* a problem — whether it existed on the ground or not — and the investigation which followed did indeed find a cause: Icing. Now, here’s the twist: This icing was *not* caused by atmospheric conditions leading to ice buildup on the exterior of the airframe — the B747 is well equipped to handle such conditions and was flying well above the weather at the time of paralysis, anyway. This was internal icing. Apparently, a leak in the aircraft galley allowed water to drip onto the aileron control cables. As the aircraft climbed to altitude and while the autopilot was engaged, the water froze on the cables and the ice formation gradually jammed the controls. As the problem worsened, it appeared to the pilots that a complete loss of roll control was imminent and their adrenaline induced strength was able to remedy things … temporarily. When the problem came again, the pilots struggled against the frozen control while they brought the aircraft down through 11,000 feet (on August 22, 1998) and the problem subsided — the ice melted away. During a post-landing inspecion, two gallons of water that had seeped through the floor of the aircraft were drained onto the tarmac.
In this case, there were no injuries and the flight ended uneventfully. Things could have turned out quite differently for the 300 plus people on board but for two facts: The destination was sufficiently south and the date was not the 22nd of December…
It’s cold out there. Stay sharp.