Ambiguous guidance to crews meant the pilots of a Jazz turboprop did not realise their approach was unstable before it landed short at Sault Ste Marie, striking light fixtures and damaging the aircraft.
Canadian Transportation Safety Board investigators found that the Bombardier de Havilland Dash 8-100’s crew opted for a VOR/DME approach to runway 30, owing to deteriorating visibility, and had identified an approach speed of 101kt.
But the runway subsequently became visible as the aircraft descended through 3,000ft and the crew was approved to continue the approach visually.
As it descended from the final approach fix, on the 3° slope, it decelerated from 204kt to 181kt as it approached 1,500ft, and the throttle levers were subsequently set to ‘idle’.
The crew had been informed that winds were gusting up to 29kt and localised weather conditions were reducing the runway visual range.
Investigators state that the aircraft maintained a 3° path between 1,000ft and 500ft as the airspeed declined from 148kt to 122kt, significantly above the target.
The crew had varied the torque setting to cope with wind conditions, and the aircraft was still flying at 124kt as it reached 200ft, and the captain – who was flying – reduced torque to idle.
As a result, the airspeed rapidly declined and the descent steepened, causing the Dash 8 to drift below the approach path. The deterioration in visibility meant the pilots lost visual references below 200ft, but they chose to continue the approach.
Torque was increased at 20ft but the aircraft touched down 450ft before the runway threshold, at a speed of 94kt, with an impact of 2.32g. The nose-gear hit an approach light 300ft ahead of the threshold.
The aircraft suffered “significant” damage arising from the hard landing and the light collision, says the inquiry, requiring replacement of the main landing-gear as well as the nose-gear and its doors.
Investigators probing the 24 February 2015 event found that the crew had set the target approach speed in accordance with Jazz operating procedures.
But the inquiry says this speed is “being interpreted” as a target to which crews should decelerate, from 120kt, once the aircraft is below 500ft.
“As a result the majority of examined approaches, including the occurrence approach, were unstable, due to this deceleration,” it states.
The crew involved in the short landing “did not recognise” that the approach was unstable, owing to “ambiguity” in the operator’s guidance and uncertainty over the required speeds.
While the loss of visual references – particularly that of the precision approach path indicator lights – should have prompted a go-around, says the inquiry, the crew instead continued the approach, and the steepened descent went “unnoticed and uncorrected”.
Source: Cirium Dashboard