Experienced pilots believe human error is behind Sunday afternoon’s tragic collision between two firefighting helicopters near Psatha, based on the evidence gathered so far. Speaking to protothema.gr, helicopter pilots said that video footage, eyewitness accounts and the information currently available all point towards human error as the likely cause.

Until the investigation is complete and the authorities issue their official findings on the cause of the disaster, however, all scenarios remain open.

The Hellenic Police (ΕΛ.ΑΣ.) has taken charge of the preliminary inquiry into the circumstances and causes of the collision. Following an order from the competent prosecutor, all the preliminary investigative procedures required to gather evidence and establish the exact circumstances of the incident are under way, police said. The site has been cordoned off and is being guarded by police while the investigation continues, after which the resulting case file will be forwarded to the relevant Prosecutor’s Office.

The shocking video of the collision raises more questions than it answers. The two helicopters appear to move towards each other, with one descending to the other’s altitude while the second accelerates forward to meet it, as if neither crew was aware the other aircraft was in the area.

In any case, pilots explain, one helicopter’s belly struck the other’s rotor after its water intake hose first became entangled in the main rotor disc. As pilots are fond of saying, a helicopter crew’s life hangs from a single rotor. So what happened?

Scenario one: misjudgement

According to reports, both crews were made up of experienced pilots with more than 3,000 flying hours on Bell helicopters. Experienced pilots told protothema.gr that only the most capable, talented and experienced crews are selected for aerial firefighting, given how demanding the conditions are.

In this case, the same sources explained, coordination between the two firefighter crews appears to have been very poor, or absent altogether. Visibility was already extremely limited because of smoke, and the two crews had no visual contact with each other, one because the other helicopter was below it, the other because it was above and slightly behind.

Given the extreme pressure, fatigue and stress crews face in trying to make as many water drops as possible, they operate at the limits of both themselves and their aircraft. Under these conditions, there was evidently also a misjudgement, with the two helicopters heading towards the same point without either crew being aware of the danger.

Firefighting helicopter pilots point out that even the presence of a third helicopter acting as a coordinator would not necessarily have prevented the tragedy, unless it happened to be at that exact location with visual contact, since radar separation typically operates at a range of around 2.5 miles and its role is to maintain separation from the wider air traffic.

There is also a strong possibility of a deviation from the prescribed altitudes, or a misunderstanding over flight path instructions, in breach of the strict vertical separation protocols that apply to aerial firefighting operations.

Scenario two: downdraught or gust of wind

Another scenario that cannot be ruled out is that one of the two helicopters was caught by a sudden gust of wind. One pilot told protothema.gr that the accident was very strange, since the two Bell 214 STs appeared to be flying in formation, with the first making a water drop on the fire. The second helicopter, which was not dropping water, can be seen descending sharply, an abrupt change in altitude that closed the gap between them until its skids touched the other aircraft’s rotor.

According to the pilot, it is very likely that the higher helicopter was caught by a gust of wind or a downdraught that forced the pilot to break formation involuntarily, descending rapidly into the space occupied by the other aircraft. Pilots say the downdraught or sudden strong gust scenario is reinforced by the fact that the pilot of the upper helicopter broke formation without warning, and by its unusually steep rate of descent, described by pilots as “not normal for this type of operation”.

It is well known that the hot air currents generated above fire fronts, known as thermals, combined with strong winds, can cause sudden loss of altitude or abrupt displacement in any aircraft, and helicopters are particularly sensitive to such disturbances. There is also the effect of downwash, the downward airflow produced by a helicopter’s rotors, which can affect the stability of a second helicopter flying in very close proximity.

Scenario three: loss of visual contact

Pilots experienced in aerial firefighting say maintaining visual contact is essential to holding formation during these operations. One strong theory here is that the crew of the trailing helicopter most likely lost sight of the aircraft ahead of it, because it was below its field of vision. The haze of smoke and ash, which creates near zero visibility conditions, is also thought to have played a part, with the trailing crew descending for a water drop unaware that their colleagues were directly in their path, resulting in the collision that severed the other aircraft’s rotor.

Once the crew realised there had been contact, they immediately pulled up, most likely also releasing the water they were carrying to gain height more quickly. It was too late, however, for the helicopter below, which, having lost its main rotor, was doomed to fall “like a stone”, killing its crew. This scenario is reinforced by the fact that Bell helicopters in any case have limited visibility downwards and to the rear. If one helicopter was positioned within the other’s blind spot, the pilots may have had no visual contact until the moment of impact.

Scenario four: a combination of factors

It would not be unusual for a pilot to misjudge wind conditions and make a wrong decision that leaves the aircraft at the mercy of gusts or air currents, leading to a fall. It should not, therefore, be considered unlikely that the tragedy resulted from a combination of errors and chance factors acting together, for example the crews failing to follow altitude protocols, or assuming they had priority and that no other aircraft was in the formation.

Scenario five: sudden pilot incapacitation

Although considered among the less likely scenarios, the possibility of a sudden medical episode affecting one of the pilots cannot be excluded. This could explain the sudden, high speed descent of one of the helicopters.

Scenario six: technical failure

The technical failure scenario currently carries the lowest probability based on the evidence available, though nothing can be ruled out until the official findings are published. Pilots explain to protothema.gr that the Bell 214 STs involved, suitably converted for firefighting use with the addition of specialised four tonne water tanks, are medium class helicopters known as “Super Transporters”.

They were manufactured between 1981 and 1993, and the largest fleet in the world is operated by the Australian company McDermott Aviation, from which Greece leases its firefighting helicopters. The 15 Bell helicopters McDermott has deployed in Greece are distinguishable by their blue and yellow livery, as well as the message “God save our pilots”, written clearly on their fuselages.

Here, sources say, there is at least a small possibility that the higher helicopter suffered a momentary loss of thrust. Even a brief fault of this kind, and the pilot’s reaction to it, could have been enough to trigger the tragedy. The question that then arises is whether the pilot deliberately released the water in the tank after the collision in order to gain height by reducing weight, or whether it was released as a result of damage caused by the impact itself.

That said, precisely because these helicopters operate in extreme and highly demanding conditions, they undergo meticulous, continuous maintenance, with thorough inspections carried out every time they touch down, both before and after each operation, which significantly reduces the likelihood of an undetected fault.