Recent events have put a spotlight on the manufacturer of a component in a mechanism that played a critical role in the Continental Connection Flight 3407 crash outside Buffalo on Feb. 12 last year. Just last week the Federal Aviation Administration issued an order that requires airlines operating a Canadian-made Bombardier CL-600 regional jet to replace a part in a mechanism with a vane that pokes out of the fuselage and senses the angle of the airflow and can trigger the plane's stall protection system. The system warns the pilots when the airplane is getting close to a stall, which occurs when the airflow over the wings is disrupted and the plane ceases to fly because the airplane is slowing too much and its nose is too high.
The FAA's order, called an airworthiness directive (AD) does not apply to the type of airplane in the Continental Connection crash, a Bombardier Dash 8 Q400 turboprop. But the manufacturer of the faulty part identified in the AD, Thales, also made at least part of the stall protection system on the Q400, according to a note in one of the National Transportation Safety Board's reports on the Buffalo crash.
The Continental Connection flight, operated by Colgan Air, left Newark with 49 passengers and crew, who all perished. The Q400 crashed as it was preparing to land at Buffalo airport at around 10:15 pm after its stall protection system set off a stick shaker in the cockpit, making the control column vibrate. The airplane was not actually stalling, although it was slowing quite rapidly, but the pilot reacted to the stick shaker in the wrong way, hastening the stall and losing control of the airplane, the NTSB found in a final board meeting and vote last month.
Thales, a French holding company, suffered a blow last year when the FAA ordered some Airbus operators to replace a Thales airspeed measuring device with one made by Goodrich. The device, called a pitot tube, is thought to have malfunctioned on an Air France Airbus before the jet crashed into the Atlantic Ocean in June on a flight from Rio de Janeiro to Paris, killing 228.
Continental Connection 3407 was flying in icing conditions and its de-icing equipment had been on for most of the flight to clear the wing leading edges and heat the windshield. Despite this, about six minutes before the crash the cockpit voice recorder recorded the pilot and first officer saying they saw a lot of ice on the windshield and the leading edge of the wing. The NTSB nonetheless decided there had been minimal ice on the plane.
The Q400's stall protection system was set for the icing conditions to alert the crew early to an approaching stall, but neither the pilot nor the first officer noticed the airspeed was declining to where it met a low-speed cue, which together with other data, including the angle of the airflow measured by the vane mechanism, activated the stall protection system.
The AD represented the FAA's endorsement of previous findings by Bombardier and Canadian transportation authorities that a certain batch of Thales parts was faulty, risking freezing in low temperatures, which "can result in early or late activation of the stick shaker and/or stick pusher" in the Bombardier CL-600, which in turn could lead to the pilots losing control of the airplane. "The FAA has found that the risk to the flying public justifies waiving notice and comment prior to the adoption of this rule," the agency stated.
This was not the first AD aimed at Bombardier's Thales angle-of-attack transducers, to give the parts their technical name. Two were issued last year alone, and a third AD last year targeted a Bombardier stick pusher, another part of the stall protection system. All of the ADs concerned variants of the CL-600 jet, not the Q400 turboprop.
In June 2005 the stick shaker unexpectedly activated in an Air Canada Jazz Bombardier CL-600 as it flew near Colorado Springs en route from Houston to Calgary, Alberta. The event occurred at cruise altitude, where temperatures drop far below zero. The pilots dealt with the interruption and the flight continued and landed safely. The NTSB, in an incident report, noted that it had not been able to determine why the stick shaker had activated.
The NTSB did not fault the operation of the stick shaker in the Continental Connection crash, putting all the blame on the captain and first officer for losing control of the plane. Capt. Marvin Renslow's lack of cockpit management skills, his iffy training record, his breaking of the rule that bans nonessential conversation below 10,000 feet, even his sleeping in the crew lounge to save money, were all used to make him look a complete doofus. But one of the Colgan pilots interviewed by the NTSB hinted that crews were wary of the possibility the stick shaker might activate as they were slowing the airplane to land in icing conditions.
Last week's AD, which becomes effective March 24, clearly states that the activation of the stick shaker by itself can at times put an airplane in danger -- without regard, presumably, to the pilots' skills or professionalism.