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Dash 8 crew erroneously thought convective activity was not a factor in Mont-Joli approach incident: TSB


August 16, 2017   by Canadian Underwriter


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A combination wind shear and turbulence was one factor in a 2016 incident in Quebec in which a pilot had “temporary difficulty” controlling a Dash 8 below 2,000 feet, the Transportation Safety Board of Canada said in a recent investigation report.

On Feb. 3, 2016 a DHC-8-102 operated by Air Canada Express was approaching Mont-Joli Airport, about 30 kilometres northeast of Rimouski.

Shortly after 7:00 p.m., when the Dash 8 was descending through 2,480 feet, the airplane “encountered moderate turbulence” and exceeded its maximum landing gear extended speed of 172 knots, TSB stated in a report released Aug. 8, 2017.

There were no injuries or property damage.

The Dash 8 – enroute from Montreal-Trudeau International airport in Dorval – was about six nautical miles from the Mont-Joli runway threshold. The pilot “disconnected the autopilot, immediately levelled off” and resumed the descent once the speed dropped to 160 knots, reported TSB, a separate agency from Transport Canada that investigates accidents and incidents in railways, pipelines, marine and aviation.

During the turbulence, the pilot “felt a sudden change in elevator force and perceived this as a reduction of elevator control effectiveness,” TSB said in the report.

The crew had been warned of an area of freezing rain and “severe icing” below 6,000 feet, in an area 30 nautical miles west of Mont-Joli, but TSB found there was no “significant ice accumulation” while approaching the airport.

“The landing gear extended overspeed occurred because the aircraft encountered significant increased performance shear while flying out of a low-level jet with the autopilot engaged in vertical speed mode,” TSB stated in its investigation report. “The combination of turbulence and shear contributed to the temporary difficulty with aircraft control effectiveness on approach.”

A low-level jet stream is one cause of “hazardous low-level wind shear,” which is “a change of wind speed and/or direction over a short distance, including updrafts and downdrafts,” TSB noted.

Wind shear was a factor in a 2014 incident at Montreal-Dorval, TSB said in a separate investigation report, released March 28, 2017. An Airbus A330 – arriving from Frankfurt, Germany – drifted and damaged runway lights while landing in heavy rain at Montreal.

In that report, TSB reiterated a recommendation made in 2007 – in a report on an accident in 2005 involving an Air France plane at Toronto International – that Transport Canada “establish clear standards limiting approaches and landings in convective weather for all air transport operators at Canadian airports.”

TSB did not specifically cite a lack of clear standards as a factor in the Mont-Joli incident in February, 2016, but the board states on its website that Transport Canada’s response to the recommendation for clear standards is “only partially addressed.”

Transport Canada said in 2010 in a paper to ICAO that Canada “should not act alone in developing a strategy” on regulations related to flight in convective weather, TSB says on its website.

In its report on incident involving the Dash 8 in February, 2016, TSB noted that the turbulence decreased after the pilot had difficulty controlling the airplane and that the pilot was able to land “with no further difficulty.” But TSB added the crew was “unaware of the presence of convective activity on approach and did not use the weather radar because they did not think that convective activity was a factor during the occurrence flight.”

Air crew flying near a thunderstorm “can expect to encounter erratic wind and gusts, squalls (violent wind blasts), turbulence, extremely violent rain, low visibility, hail and lightning,” TSB warned March, 28, 2017 in its investigation report into the 2014 incident involving the Airbus that drifted while landing in Montreal. “Furthermore, there is no correlation between the appearance of a thunderstorm and the intensity of its events.”

A “lack of definitive, real-time wind shear hazard information,” was one factor in an accident in 1985 in Texas that killed 135, the U.S. National Transportation Safety Board said at the time. On Aug. 2, 1985, a Delta Air Lines L-1011 broke apart after hitting a car and then two water tanks while landing at Dallas/Fort Worth International Airport. The L-1011 was landing “through the rain shaft beneath a thunderstorm” when it entered a microburst, NTSB said.

Wind shear was also cause factor in an August, 2016, accident at Dubai International Airport, when an Emirates Boeing 777 hit the runway as its landing gear was still retracting. At the time, The Associated Press reported that one firefighter was killed responding to the accident, and an additional 24 people were injured, including an Emirates crew member treated for five days in hospital due to smoke inhalation.

NTSB cited wind shear as a probable cause in a 1982 accident near New Orleans, when a Boeing 727 crashed into a residential area after takeoff. NTSB said at the time, there was a ceiling of 4,100 feet with visibility of five miles in moderate rain showers, with cumolonimbus clouds overhead.  The airplane, operated by Pan American, had climbed to between 95 and 150 feet when it descended into a line of trees, continued about another 700 metres and crashed, destroying six homes as well as the airplane itself. Eight people on the ground, plus 145 on the plane, were killed.