Wednesday, June 3, 2009

when comets rained from the sky

Part of the reason why the tragic loss of Air France 447 has shocked us so deeply is the rarity of such occurrences in modern commercial flight. It was literally the first fatal airframe loss of a Airbus 330 passenger plane in sixteen years of service. We are shocked because it almost never happens anymore. But it is a reminder that while airline travel is statistically safe, it is not risk free. It involves the suspension of the laws of gravity via carefully honed mechanical apparatus, and any such suspension is temporary in nature. The fact that we've gotten so very good at doing it over the last sixty years does not diminish the potential for mishap.

The first jet powered passenger plane, the British built De Havilland Comet, made its public debut sixty years ago in 1949. It was certified as airworthy on January 22, 1952, and passenger flights for BOAC commenced on June 2. It was sleek, revolutionary, luxurious and fast- so very fast. It could cruise at 490 mph compared with about 315 mph for a piston engined Douglas DC-6. And the jet engines were quieter, smoother, and much simpler to maintain than their piston counterparts. The flying public was very impressed, so much so that they were willing to overlook a couple of early disasters. Twenty two Comet 1 and 1A models (with different interiors) were produced. Incidentally, the 1A was developed at the request of Air France and became their first jetliner.

It didn't take long for the first passenger jet crash in history. On October 26th of that same year, a BOAC Comet registered G-ALYZ leaving Rome failed to become airborne and crashed at the end of the runway. Fortunately no passengers were killed, but the Comet was demolished. Early press reports blamed pilot error, but this would later be revisited. In March 1953, a brand new Canadian Pacific 1A CF-CUN also failed to become airborne, this time attempting to depart Karachi, Pakistan. This time, five crew and six passengers were lost. It was again attributed to pilot error.

Another BOAC Comet, G-ALYV crashed only two months later on May 2. This time the plane was departing Calcutta in a tropical storm when, six minutes into flight, the horizontal stabilizer separated causing an airframe failure. It was questioned whether over-manipulation of flight controls might have been a factor, but in any event it was a tragic loss of forty three lives. Still the reputation of the Comet remained aloft.

And then in 1954, they seemed to rain from the sky. On January 10, BOAC Flight 781 (registered G-ALYP) departed from Rome under clear weather, ascended to cruising altitude and then fell from the sky in a fireball near the island of Elba, to the astonishment of local fishermen who witnessed the falling debris. There had been no indications of trouble, and the co-pilot was in radio contact with another BOAC flight when the conversation ceased in mid-sentence. Thirty five people were lost. The Comet was grounded as a precautionary measure- four of twenty two had now crashed.

While the Royal Navy began to recover the debris, a committee studied possible causes and decided that the likeliest event was probably fire. After making some recommendations, the Comet returned to the skies on March 23rd. Fifteen days later, on April 8, another Comet fell from the sky. This time, a BOAC Comet 1 leased to South African Airways departed Rome bound for Cairo. The plane , registered G-ALYY again climbed to cruising altitude, and then simply disappeared near Naples with 21 on board. The Comet's airworthiness certificate was revoked and a major investigation undertaken by the Royal Aircraft Establishment.

They worked tirelessly for months. They subjected an identical airframe to underwater pressurization tests in a specially built tank. This airframe, G-ALYU, suffered a failure of the pressurized skin near an escape hatch after about 3,000 cycles. They were astonished- metal fatigue causing a hull fracture on a two year old plane was almost inconceivable. They next gutted a Comet and filled it with pressure gauges, then went for a test flight. They discovered that the square corners of the windows were subject to four times the pressure they had anticipated. It began to make sense. After careful observation, recovered wreckage of G-ALYP found a fatigue crack emanating from a fiberglass window on the roof of the aircraft provided for radio signal transmission. The Comet had a fatal flaw. Actually, it had more than one. Aerodynamic testing showed it also had a flat spot on the leading edge of the wings, so that the two incidents where it failed to ascend were reclassified from pilot error to design flaw. The windows would be redesigned as oval. the wings reshaped, and the hull thickness would be increased before attempting to return to service.

By the time the Comet returned to the skies as a vastly improved model 4 in 1958, the Boeing 707 and Douglas DC8 were on the verge of starting the era of modern jet flight as we know it. The 707, more than any other, shrunk the world and "flew the seven seas" and while both aircraft suffered incidents, they helped establish air travel as the safe and reliable method of travel we rely on today.

But it is important to remember the early days when the Comet fell from the sky, and the sacrifices made by innocent lives. No one stepped aboard the Comet expecting not to return. The final moments were certainly terrifying. The only comfort comes from the fact that the knowledge gained from those early failures significantly advanced the cause of the jet airliner. We owe them all our gratitude. As saddened as we are by the recent tragedy, we can be grateful for how rare such an event has become.

1 comment:

Birdie said...

This is fascinating. Forgive me for not knowing, but is this related to your career? You speak with some authority.