TUI Belgium B738 near Amsterdam on Oct 3rd 2020, unreliable airspeed

Last Update: December 22, 2021 / 20:53:08 GMT/Zulu time

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Photo of TUI Airlines Belgium OO-JAV, Boeing 737-800 — TUI Airlines Belgium OO-JAV, Boeing 737-800 (Photo credit: Benedikt Lang / Flickr / License: CC by-nd)

Incident Facts

Date of incident
Oct 3, 2020

Classification
Incident

Airline
TUI Airlines Belgium

Flight number
OR-695

Departure
Amsterdam, Netherlands

Destination
Funchal, Portugal

Aircraft Registration
OO-JAV

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

A TUI Belgium Boeing 737-800 on behalf of TUI Nederland, registration OO-JAV performing flight OR-695 from Amsterdam (Netherlands) to Funchal (Portugal) with 189 people on board, was enroute at FL360 over the English Channel about 10nm northwest of Guernsey,CI (UK) when the crew decided to return to Amsterdam. The aircraft descended to FL350 for the return and landed safely on Amsterdam's runway 06 about 1:50 hours after departure, emergency services were in their stand by positions having been alerted to the occurrence with the statement the crew had reported unreliable airspeed.

A replacement Boeing 737-800 registration OO-JAQ reached Funchal with a delay of about 4.5 hours.

The occurrence aircraft remained on the ground until Oct 11th 2020 before returning to service.

On Nov 9th 2020 the Dutch Onderzoeksraad (DSB) reported the crew observed differences in speed and altitude indications between the captain's and first officer's instruments. When the aircraft arrived at cruise altitude the differences became bigger. After the crew had attempted to fix the problem in vain, the aircraft returned to Amsterdam's Schiphol Airport for a safe landing. A short investigation was opened by the DSB.

On Jun 3rd 2021 the DSB reported they are investigating two occurrences, this one as well as Incident: Transavia B737 at Rotterdam on Apr 24th 2021, we think we are 6500 feet, military radar tells FL110, unreliable speed and altitude on both left and right pitot systems, where unreliable airspeeds following storage due to the Corona Pandemic had occurred. As result of the investigations so far the DSB stated, that in one case the pitot covers had not been removed, in the other case the pitot pipes had not been properly reconnected, in both cases the crew were able to use visual references outside the aircraft in favourable weather conditions. The DSB stated that EASA well as Boeing had issued warning identifying safety risks of returning aircraft to service after long term storage. The DSB further stated that there is no possibility for flight crews to test the pitot systems prior to departure. The DSB subsequently argues, that the safety risk was known in both occurrences, yet, they did happen. The DSB anticipates that an increasing number of aircraft will be returned to service in the days and months ahead leading to an increase of numbers of non-standard maintenance. The incidents show, that extra attention is needed to address this risk. This is why the DSB issues an interim warning to airlines and maintenance companies of this safety risk.

The DSB reported in their Q3/2021 Bulletin: "The following four factors were contributing to this serious incident. First, the normalized maintenance practice to cover the primary static ports with readymade placards. This practice was different from the aircraft’s maintenance manual procedure. Amongst maintenance crews, the normalization led to unfamiliarity with the maintenance manual procedure and materials to be used. Second, the intention to get the aircraft into parking with the material that was at hand. Third, the low observability of the plastic and adhesive tape used, that made it difficult to notice the covers; especially in combination with low light conditions. And fourth, the expectation bias to see orange coloured covers and streamers."