• ATR aircraft had three ‘technical anomalies’ before it took off
• Investigation report submitted to Sindh High Court

RAWALPINDI: Nearly four years after the tragic incident, the Aircraft Accident and Investigation Board (AAIB) has completed investigation into crash of Pakistan International Airlines’ flight PK-661 near Havelian, which has revealed that the aircraft had three “technical anomalies” for which the airline’s engineers were responsible.

A total of 47 passengers and crewmembers lost their lives when the ATR42 plane crashed into hills about 24 nautical miles north of Benazir Bhutto Islamabad International Airport on Dec 7, 2016.

Junaid Jamshed, a singer-turned-preacher, was among the people killed in one of the most disastrous air crashes in the country’s aviation history.

Head of the AAIB Air Commodore Usman Ghani submitted the report on Thursday to a bench of the Sindh High Court (SHC) after repeated directives by the bench in a petition filed about various incidents involving ATR planes.

A spokesman for the aviation division, senior joint secretary Abdul Sattar Khokhar, said in a press release the investigation was carried out under the guidelines provided by the International Civil Aviation Organisation and were aimed at improving the safety of air travel.

According to the investigation report, the air crash was the result of three “latent technical factors”, including fracture of one of the power turbine blades of Engine 1; a broken/fractured pin inside over-speed governor; and probable pre-existing contamination inside Propeller Valve Module.

The AAIB report, which held the PIA engineers responsible for the disaster, said the aircraft remained in air for about 42 minutes before the crash.

Analysis of the digital flight data recorder indicated that the aircraft’s Engine 1 was degraded.

“The flight took off with two pre-existing technical anomalies. One anomaly was a fractured Power Turbine (PT-1) blade and the second was a fractured pin inside the Over-Speed Governor of the same side. The probable latent pre-existing condition was contamination external from the engine observed in Propeller Valve Module (PVM),” the report said.

It said most probably the PT-1 blade had fractured during a previous flight. However, this defect is not observable during regular operations.

“It was determined that the pin inside the OSG was fractured due to improper re-assembly. Metallurgical evaluation of the OSG pilot valve pin fracture surface, at Woodward, USA, determined that the pin had failed due to overload resulting from the valve being forced together using an improper re-assembly method during some unauthorised/undocumented maintenance activity,” the report said.

Continued operation with a broken pin may possibly have weakened component(s) inside OSG.

“It has been established that any of the latent pre-existing technical anomalies and probable latent pre-existing condition … alone may not lead to such a catastrophic/hazardous situation except in the presence of unusual combination and/or additional contributing factor(s).”

The report suggested that the simultaneous existence of the three “technical anomalies” made it extremely difficult for the cockpit crew to tackle the situation effectively.

“The event was unexpected and the crew was not trained for this specific sequence of events,” said the report.

It said the captain and the first officers were well-trained and had a good overall total flying hours. They led a normal family life.

Responding to the AIIB report, the management of PIA said the airline had already incorporated immediate safety recommendations, including PT blade modifications and inspections of OSG at the manufacturing facility.

Spokesman for PIA Abdullah Hafeez Khan said the management had reviewed the crash report and acknowledged that there were three latent factors that aligned together at the time of the crash. Had any of these factors happened in isolation, the consequences would not have been so devastating.

He said that during the course of the investigation, PIA remained at the disposal of AAIB for implementing the most immediate safety recommendations which were given earlier.

There has been no similar event in the industry or with the same equipment which could help PIA maintenance and training teams to simulate such a scenario.

Meanwhile, the SHC summoned the PIA and CAA officials after submission of the investigation report.

The two-judge bench headed by Justice Mohammad Ali Mazhar summoned the director for safety management and maintenance of PIA and director for airworthiness of CAA to appear before it on Dec 1.

Air Commodore Ghani informed the bench that the report was available on the website of CAA. When the bench asked about the safety of the public, he contended that clear responsibility had been fixed in the report and certain recommendations had also been given to ensure safety measures.

Ishaq Tanoli also contributed to this report

Published in Dawn, November 20th, 2020