DH8B, Nuuk Greenland, 2019
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|On 30 May 2019, a DHC8-200 departing from Nuuk could not be rotated at the calculated speed even using full aft back pressure and the takeoff was rejected with the aircraft coming to a stop with 50 metres of the 950 metre long dry runway remaining. The initial Investigation focus was on a potential airworthiness cause associated with the flight control system but it was eventually found that the actual weights of both passengers and cabin baggage exceeded standard weight assumptions with the excess also resulting in the aircraft centre of gravity being outside the range certified for safe flight.|
|Actual or Potential
|Ground Operations, Loss of Control|
|Aircraft||BOMBARDIER Dash 8 Q200|
|Type of Flight||Public Transport (Passenger)|
|Intended Destination||Kangerlussuaq Airport|
|Take off Commenced||Yes|
|Flight Phase||Take Off|
|Location - Airport|
|Tag(s)||Use of Erroneous Performance Data|
Passenger Aircraft Hold Loading
|Tag(s)||RTO decision after V1,|
Unable to rotate at VR
|Damage or injury||No|
|Causal Factor Group(s)|
On 30 May 2019, a DHC8-200 (OY-GRJ) being operated by Air Greenland on a scheduled domestic passenger flight from Nuuk to Kangerlussuaq rejected its takeoff from runway 05 at Nuuk in day VMC when it was found that the aircraft could not be rotated and it came to a stop 50 metres from the end of the runway. The aircraft was returned to the terminal and the passengers disembarked.
An Investigation into this Serious Incident was carried out by the Danish Accident Investigation Board (AIB) after the operator notified the event 90 minutes later. Data recorded on the QAR, which were the same as those recorded on the FDR, were retrieved and the raw data file, along with the CVR was shipped to the Transportation Safety Board of Canada (TSB) for decoding and downloading respectively. It was found that the CVR had not been isolated promptly enough to preserve the most recent 30 minutes of high quality audio data but the period covering the event was contained in the 2 hour data files which record the cockpit area microphone channel and a combined version of the pilots’ individual communication channels. A recording of VHF communications on the Nuuk Aerodrome Flight Information Service (AFIS) frequency were also available.
The 57 year-old Captain had 11,144 hours total flying experience which included 4,339 hours on type and the 30 year-old First Officer, who was acting as PF for the investigated flight, had 981 hours total flying experience all but 210 hours of which was on the aircraft type involved.
It was established that the takeoff from runway 05 with a full load of 29 passengers and 3 crew members on board had been preceded by a wind check of 330° at 5 knots and takeoff had been made with a 15° flap setting and with a V1/VR of 88 knots. The standard 60 knot call was followed by “V1, Rotate” called at “approximately 80 knots” upon which the First Officer applied normal back pressure to the elevator control but experienced no positive responsive feedback (aircraft rotation) and consequentially applied full aft backpressure to the elevator control. After still not being able to rotate “and considering the lack of aircraft rotation to be a result of a flight control failure”, he commenced a rejected takeoff “by retarding the power levers to the ‘DISC’ position and applying maximum anti-skid braking”. After the aircraft had been brought to a stop, the flight crew reviewed the situation and decided that nothing was preventing a safe taxi back to the apron. Whilst this was being done, the passengers were briefed and an external visual inspection for potential hot wheel brakes was requested.
The AIB oversaw operator checks of the aircraft longitudinal control systems for any defects and to confirm correct rigging in accordance with the AMM. These found “a few items to be slightly out of AMM stated limitations” and minor rigging adjustments were made. A test for correct calibration of the pitot static system was also made and found a minor discrepancy which was within the applicable AMM limitations. The Type Certificate (TC) holder then determined that none of these “minor technical deviations” would have had any significant influence on the ability to rotate the aircraft normally and the Investigation moved to examine two potentially relevant operational issues.
- 1. The conduct of the takeoff roll. It had been noted that the Captain had made the “V1, Rotate” call slightly earlier than the calculated 88 knot V1/VR at “approximately 80 knots” which had led the First Officer to apply initial backpressure to the elevator control a little prematurely. It was recognised that this, in combination with the 3 knot higher airspeed indication found during the test of the pitot static system was likely to have prolonged the First Officer’s perception of time in terms of the absence of any positive responsive feedback from his control column movement. However, even when the aircraft accelerated to an airspeed above VR, full control column backpressure had only generated a negligible increase in pitch attitude. For that reason, the decision to reject the takeoff “complied with operating procedures and potentially prevented a more severe outcome”.
- 2. The loading of the aircraft. It was decided to:
- Re-weigh the aircraft.
- Re-weigh the baggage and cargo loaded in the holds.
- Establish the actual weights of the crew, passengers and cabin baggage and the seat which had been occupied by each passenger.
- Compare the weight and balance results using standard weights assumed by the pilots’ EFB module with those from a manual weight and balance calculation using the method in the aircraft ‘Weight and Balance Manual’.
The comparison of the weight and balance output by the crew electronic flight bag (EFB) module using assumed weights with a manual calculation using actual weights found that the actual weight of the load on the aircraft for the investigated flight had been approximately 13% greater than that generated using assumed weights and had resulted in a centre of gravity (CG) which was 2.4 inches forward of and outside the envelope specified for safe flight at type certification and contained in the AFM and the operator’s OM.
It was noted that the operator’s procedures which complied with applicable safety regulations, stipulated that ground handling and cabin crew should notify the aircraft Captain if they observed a significant number of passengers whose weights, including their carry-on hand baggage appeared to exceed the assumed standard weights.
This finding led the Investigation to question the effectiveness and the strength of the current assumptions on standard weights as a valid risk-control SOP on the basis that such assumptions “are affected by, for instance, culture, subjective perception, working experience and individual training”. It was noted that the EASA had recently “de-prioritised” the commissioning of a survey of actual weights of passengers and their carry-on baggage to update one carried out 10 years ago in the face of considerable circumstantial evidence that average passenger weights may have increased.
The formal Conclusion of the Investigation was that “actual masses above standard masses for crew, passengers and carry-on hand baggage led to a CG forward of the operational aircraft CG limitations causing reduced aircraft rotation ability during the takeoff roll”.
Safety Action taken by the aircraft operator in response to the event during the Investigation was noted to have included the following:
- Revising the weight and balance CG envelope in order to cater for increased actual passenger weights.
- Implementing of seating zones when allocating passenger seats in Electronic Flight Bag module which is used to check that the aircraft load and its distribution are within limits so as to assure more control of extreme forward and aft seating compared to an ‘evenly-spread’ assumption.
- Including a standard value for wardrobe contents (crew overnight bags etc.) of 25 kg.
The Final Report was published on 26 September 2019. The Board did not issue any Safety Recommendations but did state that “taking the severity of this Serious Incident into consideration, the AIB encourages (the) EASA to reconsider their task prioritisation on this matter”.