Air France B772 near Douala on May 2nd 2015, GPWS averts controlled flight into terrain at FL090
Last Update: April 21, 2022 / 07:41:43 GMT/Zulu time
The French BEA reported in their weekly bulletin that the occurrence was rated a serious incident, the French BEA is investigating the serious incident.
Mount Cameroon rises up to 4040 meters/13250 feet MSL about 34nm westnorthwest of Douala Airport.
On Apr 21st 2022 the French BEA released their final report concluding the probable causes of the serious incident were:
The following factors may have contributed to the loss of situational awareness concerning the position of the aeroplane with respect to the terrain and to the proximity with Mount Cameroon:
- The crew’s concern to avoid storm cloud masses and the reporting with the ATC, to the detriment of monitoring the flight path. The crew significantly deviated from the filed flight plan which made the safety altitudes mentioned therein obsolete.
- The simultaneous use of both radars in Weather mode.
- The representation of Malabo airport on a chart not to scale, which did not facilitate the identification of the position of the planned route with respect to the terrain.
- The MORA safety altitudes or grid MORA not being displayed on the ND of the Boeing 777s.
- The absence of a study of the en-route phase when the operator carried out the risk assessment prior to opening the route between Douala and Malabo, leading to the risk of dangerous proximity with terrain en route not being identified.
The activation of the EGPWS alerts and the immediate reaction of the crew meant that the collision with the terrain was avoided.
The BEA reported the captain (ATPL, 18,035 hours total, 5,998 hours on type) was pilot monitoring, the first officer (ATPL, 5,076 hours total, 3,353 hours on type) was pilot flying, a relief pilot (ATPL, 15,116 hours total, 447 hours on type), first officer, was on the observer seat. In addition a member of the cabin crew was seated at the other observer seat.
The BEA summarized the sequence of events:
The crew composed of a captain and two co-pilots(3) were performing a flight departing from Malabo (Equatorial Guinea) bound for Paris, via Douala (Cameroon). The leg between Malabo and Douala, which takes about 40 minutes, was carried out at FL 90. The captain was the PM and the co-pilot, the PF.
Due to the stopover infrastructures and the short flight time of the leg, a “departure and arrival” briefing was carried out in the cockpit before take-off.
The flight file forecast cumulonimbus and visibility greater than 10 km at Malabo. At Douala, the 17:00 METAR indicated the presence of a storm, cumulonimbus and a ceiling of 1,600 ft. The TAF forecast rain showers and visibility reduced to 3,000 m as well as a ceiling at 1,300 ft between 2 May 20:00 and 3 May 06:00. The Operations Control Centre informed the crew that the storm over Douala was in the process of moving west and that two aeroplanes had just landed there.
In contrast, the precise meteorological conditions along the route were not known.
During the briefing, the crew covered the following specific points:
- The terrain on the left side of the take-off path required a right turn to be made which is the opposite to the path specified by the FMS.
- The meteorological conditions at Douala were considered acceptable. The crew had been informed by the company’s flight operations department that the zone of convective activity which was present over Douala was moving from east to west.
- The workload linked to the numerous exchanges with the ATC without a radar between Malabo and Douala was high for the PM.
The aeroplane left the gate on time at 19:53. A member of the cabin crew was authorised to fly in the cockpit and was seated on the observer seat, on the right of the relief pilot’s seat.
At 20:03, the crew took off from runway 22, initially turned right onto heading 030° to join the flight plan route and then engaged the autopilot (AP).
At the end of the turn after the take-off, the crew indicated that they observed numerous storm cells on the radar on the flight plan route and to the south. It was night, the cells were not touching, the crew could make out their shape and see lightning. The aeroplane continued its path north-east, deviating northwards from the flight plan route. The PF’s and PM’s navigation displays (ND) were in the Weather (WXR) mode(5). The scale on the PM’s ND was 20 then 40 and finally 80 NM during the climb, on the PF’s ND, it was 80 and then 40 NM at the end of the climb. The crew used the Douala arrival chart STAR RWY 30 (6-40) to navigate.
The PF saw a large red return on his ND ahead of the aeroplane and another oblong red return on their right which seemed to be “moving forward” with the aeroplane. As the PF did not understand what was causing this second return, he was not sure about its nature and decided to set his radar to Terrain mode to clarify the situation, which simultaneously increased the scale to 80 NM. He returned to Weather mode six seconds later. Following this check, he thought that the return ahead of the aeroplane was a ground return from Mount Cameroon and that the oblong red return on the right of the route was a “false return”.
Around ten minutes after take-off, the aeroplane was 6 NM north-west of Mount Cameroon. The crew indicated in their statements that the exchanges with the ATC had become dense.
The PM suggested to the PF that he take a right heading to join the start of the DME arc to runway 30 at Douala. When the aeroplane was on a heading of 61°, the PF controlled a right continuous-turn to the selected heading of 120°.
At 20:14:02, around 30 s after the start of the turn, the aeroplane was at an approximate height of 5,000 ft when the EGPWS “TERRAIN AHEAD” caution was activated for four seconds.
The two ND automatically changed to Terrain mode. Three seconds after the activation of the warning, the PF increased the selected heading to 134°. The aeroplane continued to turn right with a bank angle of around 25°.
A few seconds later, at 20:14:12, the radio altimeter height had decreased to 4,150 ft and the “TERRAIN AHEAD PULL UP” warning sounded for eight seconds. The crew indicated that the NDs turned red. In their statements, the cabin crew member in the cockpit and the PF indicated that they made out trees on the right of the aeroplane.
The PF disengaged the AP and made a nose-up input. He advanced the thrust levers full forward to obtain maximum thrust one second later. The autothrottle (A/T) was disengaged five seconds after the start of the manoeuvre.
During the eight seconds of the warning, the pitch attitude and vertical speed increased. The maximum pitch attitude was 15°. The aeroplane remained in its turn and the relief pilot asked the PF to level the wings.
The EGPWS warning ceased at 20:14:20. The bank was briefly cancelled before the turn resumed with a bank angle of around 25°. FL120 and a heading of 150° were selected.
On approaching FL110, the PM told the PF to stop climbing. The pitch attitude was held and the PM again told the PF to stop climbing on flying through FL120. The radio altimeter height reached its minimum value of 2,100 ft corresponding to an altitude of 11,500 ft. The summit of Mount Cameroon is at an altitude of 13,202 ft.
At 20:15:30, the aeroplane reached FL130. The crew resumed navigation to the ILS DME arc of runway 30 at Douala and landed without further incident.
At the conclusion of the flight crew debriefing and after coordination with the Air France Operations Control Centre, it was decided to continue the rotation to Paris with the same crew.
The BEA analysed:
Positioning error and awareness of terrain
The chart used, with an insert to show Malabo, contributed to the difficulty in having an exact representation of the situation. It did not facilitate the representation of the flight plan with respect to elements present on the chart, notably Mount Cameroon. The short flight distance encourages the use of this chart which simultaneously shows the departure and arrival airports. Furthermore, the grid MORA is not displayed on the ND; it might have alerted the crew to the safety altitudes of the area being flown over. All of these factors led the crew to incorrectly identify the actual position of the aeroplane with respect to the terrain. The safety altitudes indicated in the flight file did not allow the crew to identify other terrain-related risks on the planned route. This could have resulted in the crew not being aware that the altitude of the surrounding terrain was higher than their en-route altitude, usual for this leg, but exceptional for a “standard” en-route phase on a Boeing 777.
Using the two NDs in weather radar mode, the crew interpreted the return generated by the cloud mass ahead of the aeroplane as a return from Mount Cameroon. The return from Mount Cameroon was considered as a false return.
These factors led to a positioning error which led the crew to turn the aeroplane towards Mount Cameroon when they thought they were joining the DME arc of the approach chart.
Crew cooperation and task sharing
The crew were composed of a captain and two co-pilots, one being a relief pilot due to the delayed departure of the aeroplane.
The captain asked the relief pilot to particularly monitor the flight, acting as his eyes and his ears. The relief pilot shared in the subjects of concern imposed by the management of the flight, namely avoiding the storms, as indicated by the cabin crew member in the cockpit who explained that he saw the three crew members “bent over” the weather radar. In this context, no crew member detected the fact that avoiding the cumulonimbus had led them to significantly deviate from their flight plan, making the safety altitudes specified therein, null and void.
The PF temporarily used the Terrain mode of the ND due to doubts about the identification of a red mass on the right side of the path. These doubts were not explicitly mentioned and were therefore not cleared up. The crew thus remained in their position error, contributing to them approaching Mount Cameroon. The PF’s careful start of the turn was symptomatic of his continuing hesitation as to the nature of this red mass.
The operator carried out a route study prior to flight operations between Douala and Malabo. This study was based on the risk analysis at the departure and destination airports. This analysis resulted in the identification of risks linked to the presence of terrain at both Malabo and Douala. However, there was no risk assessment of the en-route phase. On short routes, the en-route phase can be carried out at low altitudes, potentially below that of the terrain, as illustrated by this incident.
The en-route phase can thus present particular risks which on being identified by the operator, can allow crews to better take them into account. The route study, carried out beforehand by the operator, should identify these risks, bring them to the crews’ knowledge and propose mitigation measures. The crews’ situational awareness would thus be reinforced, this being all the more important in that keeping flight threats up to date cannot be guaranteed in a dynamic phase such as avoiding storm cells.
Carrying out emergency manoeuvre
Immediate compliance with the emergency procedure associated with an EGPWS “PULL UP” warning is primordial to maximize the terrain avoidance manoeuvre. The emergency manoeuvre does not guarantee, however, that the terrain will be cleared, which is why it is important to benefit from the steepest climb gradient possible. The procedure allows the stick to be pulled until the stick shaker or buffet appears, significantly reducing the stall margins. These will be all the more preserved when the aeroplane’s wings are level. It is possible to continue a turn when this type of warning occurs, when the crew has good situational awareness, notably in the day when the terrain which caused the warning is visible.
The emergency manoeuvre was carried out without delay by the PF and monitored, in particular, by the relief pilot who reminded him to level the wings. Not all the training scenarios provide for this manoeuvre to be carried out in a turn, meaning that levelling the wings is not part of the systematic checks made by the instructors.
FKKD 022300Z 00000KT 9999 TS BKN013 SCT016CB OVC100 24/23 Q1011 NOSIG
FKKD 022200Z 00000KT 8000 TS BKN013 SCT016CB OVC100 24/22 Q1011 NOSIG
FKKD 022100Z 04004KT 6000 -TSRA SCT003 OVC013 SCT013CB 24/22 Q1012 TEMPO 4000 -TSRA
FKKD 022000Z 10004KT 6000 -TSRA SCT003 OVC013 SCT013CB 25/24 Q1010 TEMPO 4000 -TSRA
FKKD 021900Z VRB15KT 2000 TSRA OVC013 SCT016CB 28/26 Q1009 TEMPO 1400 +TSRA
FKKD 021800Z 22008KT 9999 TS BKN016 FEW020CB 30/26 Q1007 TEMPO VRB15KT 4000 -TSRA
FKKD 021700Z 22008KT 9999 TS BKN016 FEW020CB 30/26 Q1007 NOSIG
FGSL 030000Z 27006KT 8000 TS SCT008 FEW016CB BKN060 25/24 Q1009 NOSIG
FGSL 021900Z 00000KT 9999 TS FEW010 FEW020CB 29/26 Q1010 NOSIG
FGSL 021800Z 27006KT 9999 FEW010 FEW020CB 28/25 Q1009 NOSIG
FGSL 021700Z 24004KT 210V270 9999 FEW010 FEW020CB 30/24 Q1008 NOSIG
FGSL 021600Z 23003KT 9999 TS SCT010 FEW020CB 30/26 Q1008 BECMG NSW
This article is published under license from Avherald.com. © of text by Avherald.com.
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