Reasons behind the crash (Analysis)
8 Dec, 2016
Pakistan International Airline’s flight PK661 operating from Chitral to Islamabad on an ATR 42-500 with 42 passengers and 5 crew members crashed yesterday near Havelian, some 80KM north of Benazir Bhutto International Airport.
No one survived the crash.
While it is too early to list down the exact reasons behind the crash, we will try to analyze available information and try to come up with possible reasons for the crash of flight PK661.
What We Know About PK661 Aircraft?
ATR 42-500 is one of the most recent versions of ATR aircraft. Its first delivery was made in 1995 while the flight in question, PK661 with Registration AP-BHO, was delivered to PIA in May 2007.
ATR 42-500 comes with six-bladed propellers powered by PW127E engines rated at 2,400 shp (1,800 kW) for improved hot and high performance and increased cruise speed.
ATR 42-500 engines are certified to be safe, strong and solid performer in a variety of conditions.
It had flown 18,740 hours before it crashed yesterday.
Crashed aircraft details are as following:
Aircraft Type: ATR 42-500
Certificate of Registration Number: 751
Registration Date: May 18, 2007
Operator/Owner: Pakistan International Airlines (PIA)
Construction Number: 663
Year Built: 2007
First Flight: May 3, 2007
Test Flight Registration: F-WWLU
Delivery Date: May 14, 2007
Aircraft Name: Hasanabdal
Weather conditions at the time of crash in the area were quite normal.
Below are weather values for Havelian at the time of the crash:
Time of incident: 4:10PM
Temperature: 23.0 °C
Dew Point: 10.0 °C
Air Pressure: 1016 hPa
Wind Direction: SE
Wind speed: 7.4 km/h
Azam Saigol, Chairman PIA, confirmed during a press conference that AP-BHO was Class-A checked just one month ago, indicating that the aircraft was in perfect condition.
While there was one instance of engine failure of the same aircraft back in 2014, it was replaced with a new engine and since then AP-BHO had operated smoothly without any issues being reported.
For flight PK661, there were 47 passengers on-board the ATR 42-500, indicating that the plane was pretty much with-in its load capacity.
Chairman PIA confirmed that flight PK661 was piloted by Salehyar Janjua, with flying experience of more than 12,000 hours.
Pilot of ill-fated PK661 had extensive experience of flying in northern areas, which means that he was well versed with the route and conditions where PK661 crashed.
Engine Failure And Ultimately the Crash!
Air Control Tower confirmed that flight PK661 signaled an engine failure at 4:12PM. Till the time the flight PK661 was flying smoothly at 13,375 feet.
However, as soon as the engine failure was reported, aircraft started descending — gradually at first.
Let’s have a look at flight data of PK661:
The initial descent was gradual and seemingly controlled, until the aircraft reached 12,800 feet. This is when aircraft gained altitude of 50 feet and reached 12,850.
However, it started descending again — in a non-symmetrical manner — and reached 12,175 feet.
Flight PK661 must had become imbalanced by then as it lost irregular altitude during next few moments.
Flight started to bump starting 4:12PM — this is when it approached ATC and reported engine failure
PK661 kept loosing altitude and lost 2,000 feet (gradually) with-in next 60 seconds
Then a free fall and another 1,800 feet were lost with-in a millisecond
PK661 Slightly stabled for few miliseconds and then lost another 2,000 with-in a millisecond
PK661 fell freely for over 4,000 feet to reach 8,250 feet with-in moments
PK661 gained some control and glided for few seconds before another free fall at around 4:13PM before disappearing from the radar
Here is what we are sure about:
One engine had failed
PK661 fell freely
PK661 was damaged structurally
Since PK661 fell freely, we can say with certainty that aircraft was not in-tact and it had lost its shape and failed to glide.
It must be noted here that ATRs can glide even if both engines are switched off / malfunctioned. Since PK661 was flying at around 13,000 feet — had it been in-tact — it could glide some 15-25KMs before hitting the ground.
However, an aircraft will fall freely if there’s any structural damage as hampered aerodynamics will not allow the aircraft to glide with a gradual descent.
Since we know that at least one engine had failed, there’s a chance that it splashed and damaged the wing attached to it, affecting the aerodynamics of the aircraft which ultimately brought it down with-in seconds to and resulted in a crash.
It must be noted here that pilots have a way of shutting down the engine. But before that you need to descend and reduce speed to match the aerodynamics of the situation the aircraft is in, which the pilots did — and is seen in the graph above.
You simply do no shut the problematic engine immediately. Instead, you bring the aircraft to a certain altitude and speed to make sure that the remaining engine is able to handle the load and aerodynamics.
And while the pilot was trying to do so, the failed engine probably caught fire or more likely exploded and damaged the wings.
It must be noted that there are steps involved in stopping a mid flight ATR engine and it includes performing certain checks, such as shutting down the fuel supply, shutting down the engine itself and so on.
Here is what seemingly happened:
Pilot reduced speed, dropped altitude — clear from above graph
Free Fall Due to Structural Damage
Pilot shut down the engine and
Shut down the malfunctioned engine, however, it was too late and it had exploded before that and damaged the wing
Stopped the working engine, and throttled the malfunctioned engine that triggered the explosion and damaged the wing
Here’s what seemingly didn’t happen:
Aircraft was a good height/speed, and chances of stall are unlikely
Aircraft didn’t run out of fuel, clear from the burns at the crash site
So the information we have so far indicates that the engine exploded and damaged a wing, impacting the aerodynamics and forced the aircraft to fall freely to ground with-in seconds of the incident.
It must be noted that complete details about the PK661 crash, with an authoritative conclusion is only possible after decoding more info from FDR, Cockpit Voice Recorders and other flight data recorders.
A conclusive investigation is must here, and reasons must be determined that brought down the PK661. This is not important for PIA only but for ATR as well, to avoid any future accidents.
It must be mentioned here that there are over 1,500 ATRs in service today — with almost similar specs — and a only a conclusive investigation will ensure safe travel on ATRs in the future.