Malaysia B738 near Kuala Lumpur on Apr 3rd 2022, pitot static system failure causes upset

Last Update: March 3, 2024 / 15:29:21 GMT/Zulu time

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Photo of Malaysia Airlines 9M-MLS, Boeing 737-800 — Malaysia Airlines 9M-MLS, Boeing 737-800 (Photo modified based on photo from Alec Wilson from Khon Kaen, Thailand / Wikimedia Commons / License: CC by-sa)

Incident Facts

Date of incident
Apr 3, 2022

Classification
Incident

Airline
Malaysia Airlines

Flight number
MH-2664

Departure
Kuala Lumpur, Malaysia

Destination
Tawau, Malaysia

Aircraft Registration
9M-MLS

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

A Malaysia Airlines Boeing 737-800, registration 9M-MLS performing flight MH-2664 from Kuala Lumpur to Tawau (Malaysia), was enroute at FL300 about 110nm east of Kuala Lumpur already over the coast of Malaysia to the South China Sea when the aircraft pitched up with the autopilot disconnecting due to a wrong airspeed indication, the crew counteracted to maintain control of the aircraft. The aircraft subsequently performed a controlled descent to FL130 levelling off at FL130 15 minutes after leaving FL300 (average rate of descent 1130 fpm) and returned to Kuala Lumpur for a safe landing about 2 hours after departure.

A replacement Boeing 737-800 registration 9M-MSB reached Tawau with a delay of about 4.5 hours.

Passengers told Malaysian media initially, that the aircraft had been in turbulence at FL310 when it suddenly, within seconds, lost 7000 feet to FL240 causing them to float out of their seats and to fear for their lives. That narrative was clearly disproven by radar data (the aircraft had never been at FL310 and had never maintained FL240, no drop of 7000 feet within seconds was recorded), while the air return indicated there had indeed been some sort of a problem. Neither Malaysia Airlines nor the Civil Aviation Authority of Malaysia responded to inquiries by The Aviation Herald however.

Malaysia Airlines initially announced the aircraft had suffered a "technical problem compounded by bad weather en route".

In a media statement on Apr 10th 2022 the Civil Aviation Authority of Malaysia reported that CVR and FDR of the occurrence aircraft had been secured and had been analysed. Based on the FDR data a malfunction of the pitot static system was discovered that caused erratic speed indications prompting the autopilot to disconnect and the aircraft to substantially pitch up. The crew reacted correctly pitching the aircraft down, an abrupt input from the flight crew was seen on the FDR. These maneouvers correspond with the pilot post flight reports as well as some of the passenger experiences. These maneouvers were compounded by bad weather which caused passenger discomfort in the cabin. The initial actions taken by the crew as well as the execution of the abnormal recovery checklist as per standard operating procedures were sufficient based on the initial investigation results. Malaysia Airlines completed a review of the pitot static systems including pitot heating on their fleet, the occurrence aircraft remains currently grounded pending a review by Boeing.

Malaysia's AAIB released their final report concluding the probable causes of the serious incident were:

Causes/Contributing Factor/Probable Causes

AAIB will look into the three (3) domains of Aviation Safety while conducting the investigation. Three domains of Aviation Safety were:

a. Safe Product
b. Safe Operations
c. Safe Air Transport System

- Safe Product
+ All four (4) components associated with the occurrence have been removed and sent to the authorised facility to check on their serviceability.
+ As a result, all components were found to be working as per normal.

- Safe Operation

+ No maintenance issue linked to the event was identified.
+ There was a force to the Control Column that disconnected the AP1.
+ CRM was not carried out effectively and accordingly. The PIC made an abrupt movement by pushing the control column down.
+ Flight crew pairing could have contributed to the occurrence.

- Safe Air Transport System

+ The meteorological information provided by meteorological office was correct.
+ All navigation aids were operating normal.
+ MOC had respond to the occurrence appropriately.

- There was a possibility of human error involvement where the popped CB was overlooked and not pushed in during visual inspection prior to departure by flight crew.

- As mentioned by the FO, weather conditions require them to avoid the clouds during their flight enroute to Tawau. FDR data shows that Pitot Heat Left was off throughout the flight, as shown in (Figure 24), and the aircraft flew through clouds at 25000 ft. Due to that, it was possible that the ice would have gradually built up on the Capt. Pitot probe. The blockage had resulted from losing heating on the Capt. Pitot probe that flies through an icing condition. The ice build-up on the probe would have caused the discrepancy in the Capt. IAS indication.

The drop in the Capt. IAS indication, compared to F/O IAS, would have
triggered the Master Caution warning.

- From the FDR data, the flight crew's abrupt flight control movement was suspected to be present during the IAS disagreement event.

The AAIB analysed:

Crew Resource Management (CRM)

During the first IAS DISAGREE event at 1507 LT, the PIC did not call out or crosscheck the speed difference with the FO. From the PIC recorded statement, it was found that the PIC made an abrupt movement by pushing the control column down when the PIC saw his speed trend going down and his active bar going up.

The PIC only communicated with the FO after the PIC glanced at the FO's instrument when the AIS Disagree alert and ALT Disagree alert came out and asking the FO to crosscheck his instrument.

In summary, the PIC reaction by pushing the control column down resulted the aircraft experiencing a sudden drop without communicating with the FO, which could have been avoided if proper CRM had been carried out.

Simulator Test

A simulation session was carried out on B737-800W Flight Simulation Training Device to simulate the occurrence of "IAS DISAGREE" and "ALT DISAGREE". The simulation was to observed how the system responded to the simulated occurrence.

From the FDR data, AAIB found that autopilot A was engaged at the time of the incident, and the physical input on the flight control column disconnected the autopilot.

However, from the interview with the flight crews, there was no input from them. AAIB Investigator have tested at the Simulator where a force has to be applied to the Control Column to turn off the autopilot.

In summary, A force is needed to deactivate the Autopilot. The physical input to the flight control column disconnected the Autopilot, and it has been tested at B737-800W Flight Simulation Training Device where the autopilot system has been disconnected with force to the control column. Master Caution was ON during occurrence.

Training syllabus – Upset Prevention and Recovery Training (UPRT).

MAB has the UPRT training syllabus into four (4) Modules. However, the training syllabus in all four (4) modules did not cover the “AIS Disagreed and ALT Disagreed” condition simultaneously.

Flight Crew Manning (pairing)

From the recording statements, the PIC hours on the aircraft type were about 1515 hours, and the FO hours on the aircraft type were approximately 190 hours. The flight crew pairing could contribute to the occurrence. With minimum flying hours on aircraft type, both flight crew should be paired with more experienced crew where CRM can be appropriately exercised call out or crosscheck between crews during the first IAS DISAGREE event at 1507 LT).

Capt. Pitot probe heating status was in OFF condition at the start of the engines and throughout the flight.

FDR data show that the Capt. Pitot probe heating status was in OFF condition at the start of the engines and throughout the flight. The heating status in OFF condition is equivalent to no heating being applied. When the aircraft flew through clouds at 25000 ft, it was possible that the ice would have gradually built up on the Capt. Pitot probe. The blockage had resulted from losing heating on the Capt. Pitot probe where the aircraft flies through an icing condition. The ice build-up on the probe would have caused the discrepancy in the Capt. IAS indication