Two planes that crashed on Saturday near Bivio in the Swiss canton of Graubünden may have collided in the air.

Because both wrecks and the five fatalities - the pilot of the glider and the pilot and three passengers on board the engine - were found just one kilometer apart at an altitude of 2,700 meters.

The propeller plane, a Robin DR400, was discovered by the rescue teams only by chance while looking for the glider.

Did the two planes collide?

In the uncontrolled airspace in the mountains, up to a certain height is always flown in visual flight. This means that every pilot has to look out of his cockpit and keep an eye out for other planes and helicopters as well as for large birds. Seeing and being seen is the name of the principle that works very differently than with airliners. Because they are guided by a pilot on a safe course and at a reserved altitude away from other commercial aircraft.

In general aviation aircraft - i.e. the usual Cessna, Piper, helicopters, gliders or ultralight aircraft - there are also collision warning systems. Unlike in commercial aircraft, however, these are not compulsory, but only to be installed voluntarily. Glider pilots usually have a Flarm-type collision warning system on board. It came about after several fatal collisions, some of which were fatal, because in the past several glider pilots often circled in an updraft zone at the same time, sometimes could not see each other and collided. The Flarm device emits an acoustic alarm tone. A visual indication on a display shows where the other aircraft is, but only if it also has a Flarm system on board.In the meantime, many owners of propeller-driven aircraft also have these systems on board in order to detect gliders and powered aircraft in good time.

Glider pilots are parachute carriers

Because a white glider that may come out of the sun in a bright sky is extremely difficult for other pilots to see. And conspicuous strobe lights are unusual in gliders because they need a lot of energy from the on-board battery. Motorized aircraft, on the other hand, are equipped with position lights at the tips of the wings and with a strobe light. For safety reasons, glider pilots therefore wear a sit-down parachute. Because in the event of an emergency, such as the blocking of the controls, the loss of aircraft parts or in the event of a collision, they have to throw off the canopy, jump out of their machine and deploy the parachute. The four people killed on board the motor machine in the accident in Bivio had no parachutes. Because these are of no use in a propeller-driven touring plane,because in an emergency opening the doors and getting out of the machine against the wind would not be possible at all. Only pilots of powered aerobatic planes also wear a parachute for safety reasons.

The investigations of the Swiss Security Investigation Office will now show whether the two aircraft actually collided in the air above Bivio. Because in a collision in the air, parts or at least splinters of paint from the other machine would be found on both wrecks. Since no aircraft was on fire, the chances of the accident investigators being good not only to find out whether the two planes collided, but also at what angle. Such accident reports should not primarily lead to blame - rather, pilots or aircraft and helicopter manufacturers can learn from these accidents and draw constructive conclusions.

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