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ASN Wikibase Occurrence # 244935
Last updated: 15 October 2021
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Date:07-FEB-2018
Time:18:40
Type:Silhouette image of generic B738 model; specific model in this crash may look slightly different
Boeing 737-8K2 (WL)
Owner/operator:Transavia France
Registration: F-GZHO
MSN: 43880/5270
Fatalities:Fatalities: 0 / Occupants: 3
Other fatalities:0
Aircraft damage: None
Category:Incident
Location:Norwich Airport (NWI/EGSH) -   United Kingdom
Phase: Take off
Nature:Ferry/positioning
Departure airport:Norwich Airport (NWI/EGSH)
Destination airport:Paris-Orly Airport (ORY/LFPO)
Investigating agency: BEA
Narrative:
The crew had ferried an aeroplane from Paris-Orly airport to Norwich Airport, U.K. and had to bring back to a Boeing 737-800, registered F-GZHO, which had just come out of a maintenance inspection. For this return flight, only an airline company employee who had supervised the maintenance operations was on board and would be in the cockpit for the flight.
The aeroplane took off from runway 27 at 18:40. It was night, the conditions were VMC and the captain was PF. During the take-off run, the captain called out “check” a few moments before the first officer called out “80 knots”. The crew continued the take-off and at roughly the moment when the captain carried out the rotation, the IAS DISAGREE alert message appeared on both PFDs. The crew called out the appearance of the alert and quickly saw that the right PFD was giving erroneous speed indications while the left PFD and standby airspeed indicator were supplying identical information. During the initial climb, the AOA DISAGREE and ALT DISAGREE alerts were also displayed on the PFDs. The captain decided to continue the flight as the speed information displayed on his PFD was correct. He also decided to postpone carrying out the checklists as the workload at this point of the flight was very high due to a large amount of traffic in the London TMA. The crew observed during the climb that the altitude displayed on the right PFD was also erroneous and that the differences in speed and altitude between the two PFDs was increasing. At their cruising altitude of FL200, the first officer indicated that the difference was 2,000 ft and between 30 and 40 kt, the values on the right side being lower than those on the left side. The crew then carried out the AOA DISAGREE and ALT DISAGREE checklists followed by the IAS DISAGREE checklist which referred them to the Airspeed Unreliable procedure. Both pilots consulted this procedure but did not apply it as they had identified the erroneous indication and knew that the left PFD indication was correct. They nevertheless checked that the speed indication of the left PFD - which they considered correct - was consistent with the Flight with unreliable airspeed table. They kept the autopilot (AP), the flight directors (FD) and the auto-throttle (A/T) engaged. Once the checklists had been carried out, the crew carried out an assessment and decided to continue the flight to Paris-Orly. They did not transmit a PAN PAN message and they did not inform the ATC of their problem. During the descent, the captain contacted the Transavia maintenance department to report the problem encountered and request work by a maintenance technician. For the approach,
the crew checked in the QRH for the thrust and pitch to be set. The pilots decided to increase the approach speed by 10 kt in order to have a sufficient indicated airspeed on both PFDs, given that the performance of the aeroplane with the increased speed was compatible with the length of the runway at Paris-Orly. The aeroplane landed without incident. The captain recorded the alerts which had occurred duringthe take-off in the AFL. A technician inspected the aeroplane during the night but did not find any problem.

On the subsequent flight the next day, the aircraft suffered from the same issue. This time the flight crew turned back to Orly Airport.

Contributing factors
The following factors contributed to the dysfunction of the right AOA sensor and the display of the IAS DISAGREE, AOA DISAGREE and ALT DISAGREE alerts during the take-off of the flights of 7 and 8 February.
- The contamination of resolver 2 of the right AOA sensor by a solvent which led to a failure of the resolver and erroneous speed and altitude indications, followed by the AOA, IAS and ALT DISAGREE alerts. The investigation was not able to determine the cause of this contamination which seems to be an isolated case nor the reason why
this defect, present since the installation of the sensor on the aeroplane, led to the activation of the alerts during a post maintenance flight. However, it is possible that the handling of the sensor during maintenance exacerbated the dysfunction without the technicians realising this.
- The technician working on the aeroplane between the two flights not using the FIM. Its use would have ensured that a more complete check was carried out, the failure would have probably been detected and the sensor replaced.

Sources:

BEA
https://aviation-safety.net/wikibase/206212
http://aerossurance.com/safety-management/aoa-anomalies-transavia-b738/

Accident investigation:
cover
  
Investigating agency: BEA
Status: Investigation completed
Duration: 2 years and 9 months
Download report: Final report
Other occurrences involving this aircraft

8 Feb 2018 F-GZHO Transavia France 0 Paris-Orly Airport (ORY/LFPO) non

Media:


Images:

Photo of F-GZHO courtesy AirHistory.net


Lyon - Saint-Exupéry (LFLL / LYS)
12 September 2019; (c) Felix Goetting

Revision history:

Date/timeContributorUpdates
16-Nov-2020 18:30 harro Added
24-Nov-2020 06:25 Aerossurance Updated [Source, Embed code, Accident report]

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