Norwegian investigators have clashed with Canadian regulators by pressing for automated warnings to activate Bombardier CRJ200 wing anti-ice systems, after a Cimber Air jet stalled during departure from Oslo.
Accident investigation authority SHT has sharply criticised the need to depend on checklists to operate a single switch that could prove safety-critical in icing conditions.
"Experience with this aircraft type has shown that soft procedure-based safety barriers are too weak to solve the problem of loss of control during take-off in winter conditions," says SHT, adding that measures have not, so far, corrected a "fundamental" safety matter.
"A barrier based on the use of checklists and memory for activation is not sufficient when the consequences of forgetting the barrier may be fatal," it says.
As the Cimber CRJ200 prepared to depart on Runway 19L, after de-icing, the crew reconsidered whether runway braking and crosswinds were within limits. This discussion distracted the first officer, who was about to switch on the wing anti-ice.
"The first officer was ready with his hand on the switch, but this item was delayed and subsequently forgotten when the [take-off discussion] came up," says SHT.
During take-off, the CRJ200 rotated rapidly - at 6.1°/s, twice the typical rate - at an airspeed of 119kt (220km/h), but rolled to the right within 1.8s of lifting off. The uncommanded bank reached almost 40° at a height of 30ft (9m).
"Both [pilots] saw they were at very low altitude and headed for the snow-covered ground," says SHT. The crew countered with left aileron and rudder deflection and the aircraft's anti-stall system - a stick-shaker and stick-pusher - activated, although the stall occurred 5° below the expected stall angle.
"A catastrophic accident was prevented by the stick-pusher and the crew handling the loss of control in combination," says SHT.
There was no evidence of de-icing problems and the take-off took place within the de-icing hold time.
SHT says contamination of the wing resulted from runway spray enveloping the wing root during the take-off roll.
Only four people - two pilots and two cabin crew - were on board the 31 January 2008 flight, which was positioning for Copenhagen after diverting to Oslo.
Transport Canada, while agreeing that the CRJ is susceptible to a stall if the crew does not follow established procedures, has rejected the recommendation for non-procedural corrective action as "unacceptable".
It dismisses as "basically anecdotal" SHT's suggestion that the type has a poor safety record in such conditions, and also points out that problems of nose-wheel spray are "generic to all low-wing aircraft", not just the CRJ200.
SHT acknowledges that Bombardier has previously considered ground ice-detection systems, but the technology is "not sufficiently developed" for use on CRJ200s. It says Bombardier has also studied options for automatic moderate leading-edge heating.