2016 Luqa Plane Crash: A Detailed Look Inside the Report
Following the crash of a surveillance plane in Luqa back in October 2016 which killed all five people on board, a French board of inquiry has failed to find any cause for the dramatic turn of events.
Here’s a detailed look at the report, and what it did find.
Where’s this report from, and why did it take so long?
The report is from the BEAD, a French public body that investigates mishaps involving French state aircraft or civil aircraft contracted by the state. It’s similar to public transportation boards like the USA’s NTSB which investigate civilian accidents. This French board however only looks into military mishaps, or mishaps involving aircraft on state missions.
Since the mission was paid for by tax payers, and as is often the case in countries like the United States and France, these reports are required to be public. You can read a full version of the report in French here.
Air accident investigation reports take a long time because of their highly technical nature. Investigators don’t individually have all the knowledge required, but pool it by assembling a multidisciplinary team. Each country often has just one team, and several different investigations are likely to be going in parallel, stretching resources thin.
What was the mission?
The report only says that the heavily modified 19 seat Metroliner was set to depart for a surveillance mission. Italian aviation journalist David Cenciotti reported that similar aircraft often survey the Libyan coastline to track and document trafficking routes between North Africa and Europe used to smuggle both humans and drugs.
Aircraft undertaking such missions often have elaborate sensors fitted, which often include optic and infrared cameras, antennas that capture non-aviation radio bands like those used on ships and in walkie-talkies and even mobile phones. A number of these sensors added onto the aircraft are visible in photos. The additional weight of these sensors might play a crucial role – as we’ll see later.
Sensors fitted are marked in yellow. Image courtesy of the Aviationalist/Ruben Zammit.
Despite the aircraft not being fitted with either a Flight Data Recorder or a Cockpit Voice Recorder – traditionally both called a black box, the investigation team were able to piece together the accident sequence by using recorded images from a number of cameras on the airport. A handful of these are used by Air Traffic Controllers to verify that pilots have cleared the runways in specific hard to see spots, while others are simply operated by MIA so that enthusiasts can have a view of the apron on the MIA website.
The reconstructed sequence is as follows:
At 7:18 am, the aircraft was cleared for take-off from Luqa’s runway 13. About 30 seconds later, the aircraft had accelerated to a sufficient speed, and the flight crew began to pitch the nose up to ‘rotate’ off from the runway. Up to this point, everything was normal, with the crew retracting the landing gear, and the aircraft climbing up to a height of 190 feet.
Then suddenly, four seconds into the climb, the aircraft rolled rapidly to the right, finding itself inverted on it’s back over the runway. Reaching a maximum altitude of 260 feet, the plane began lose altitude rapidly when upside down: the crew attempt a recovery by banking to the left in a bid to re-level, but without enough time and altitude, the aircraft crashes 10 seconds after taking off, at a vertical speed in excess of 5,000 feet per minute: equivalent to 91 kilometres per hour straight down.
This is a reconstruction of the flight path the investigators pieced together from the various videos they saw.
The sequence is annotated as follows: H is the altitude in feet, Vs is the forward speed of the aircraft in knots, Vz is the vertical speed in feet per minute. Assiette is pitch angle, or the angle of the nose relative to the horizon, while Phi is the bank angle: the angle of the wings relative to the horizon.
The airplane impacted an airport perimeter wall, with the crash damaging the fence, creating a 1.5m crater in the road and burning down a number of trees. Three firefighting trucks arrived on the scene 2 minutes and 40 seconds later, and managed to extinguish the fire within 45 seconds. Sadly, the firefighters also found all 5 occupants had died.
The Investigators used CCTV footage in the absence of data from a ‘black box’
Despite them not having a flight data recorder to work with, the investigators got creative. Besides recreating the aircraft’s 10 second flight from four separate CCTV videos, as detailed above, they also used the audio tracks from some of the videos to check whether the engines were operating normally.
Shortly after staring the takeoff roll, the audiotrack of this recorded footage has a 106Hz signal which investigators say corresponds to an engine at takeoff thrust.
Using spectral analysis techniques on these sound tracks, the investigators first corrected for the different displacement from the camera in all the different videos, and checked for a frequency between 101 and 109 hertz. This specific range was deliberate. A Metroliner’s propeller rotating at full speed normally generates a 106 hertz frequency.
Using this technique, the investigators were able to determine that at least one of the engines was operating at maximum power until impact.
This 106Hz signal is present up to the final seconds of the flight, indicating that at least one engine was operating normally.
This is important because twin engine aircraft like the Metroliner are still capable of flying safely following the failure of one engine, and pilots train for engine failures on take-off meticulously in simulators: here’s an example of one such exercise in a similar sized aircraft.
Wake Turbulence and Bird strike ruled out
Clearly something else had happened. The investigators were able to discount wake turbulence from a preceding aircraft – spiraling columns of air that are left by aircraft in a manner similar to waves of wake left by boats on the sea. While an aircraft had departed 3 minutes earlier, the turbulence was calculated to have all but been dissipated by then, especially considering that the wind on the day would have of pushed this disturbed air away.
Damage due to a bird strike was also ruled out, since no birds were observed on the video. One possible factor that might have of had a role but not cause the crash was the position of the rising sun, which was right in front of the crew.
The investigation will continue to look at the engines and flight control systems – with updates coming in close to another year.
That’s a relatively sober and undramatic conclusion, but most aircraft mishap investigation reports are, with them being aimed solely at uncovering factual information that might prevent future accidents.
The Aircraft’s Special Configuration Probably Didn’t Help
The report also details that in the previous year alone modifications to the airframe – likely those earlier mentioned sensors – increased the aircraft’s weight by 52 kilograms. It’s not clear if all the sensors onboard were installed in the previous year, so the total added weight could be higher than that.
The investigators also calculated that the airplane on the day was pretty heavy, at a calculated weight of 16,082 pounds and close to its maximum take-off weight of 16,500 pounds – partly due to the aircraft carrying a full fuel load in it’s tanks.
Generally, the heavier an aircraft is, the poorer its performance. How the load is distributed also matters: in most aircraft, loading forward of the centre of gravity improves stability, while loading to the rear of the centre of gravity decreases it – most of the modifications to the Metroliner appear to be to the rear of the aircraft.
The Metroliner is also infamous in pilot communities for being unforgiving and unstable. While all of this is speculation, and not part of the report, it’s likely that the add-on sensors made an already poor handling aircraft handle even worse, which might have of contributed to the flight crew losing control in some way.
If that initial event was human error or something else remains to be uncovered at this moment.
What is certain is that the five men that perished were serving the French state in a larger pan-European attempt to increase border security and crack down on traffickers – and for this service they all deserve our gratitude.