How do helicopters park themselves?

Helicopter accident while parking: Robinson R44 in Straubing

Sometimes pilots make mistakes and immediately know what went wrong. Sometimes it takes a little longer. But sometimes it is difficult to determine what happened in the first place. Depending on the perspective and memory of those involved or not involved, everyone tells something different; the actual events can hardly be reconstructed - and become a matter of opinion. One such case occurred on March 30th this year in Straubing, Lower Bavaria.

It is a sunny spring day with optimal visual flight conditions. The wind blows rather cautiously with three knots from different directions. In the late afternoon, a Robinson R44 Raven II helicopter hovers in Straubing-Wallmühle for landing. The pilot completed a briefing flight on the piston-powered light helicopter. His flight instructor is sitting to his right. The flight led from the Landshut airfield to Straubing. Up to this point, the briefing went without any particular incident. The R44 lands at 5:39 p.m. and then floats further east along the hangar. Then he turns west to get to his parking space between the halls.

Accident of the R44: The pilots see it differently

What happens in the following seconds has not yet been fully clarified and cannot be clearly reconstructed from the reports of the crew and the observations of some witnesses. Three outsiders report that the machine floated between the halls at a height of about one and a half meters. In front of one of the halls, the helicopter suddenly made jerky movements to the left in the direction of the hall gate. Then the main rotor touched the gate and parts of the main rotor were torn off. The helicopter finally came to a standstill on the runners and caught fire. The pilot and flight instructor were able to leave the machine just in time and got away with minor injuries.

The crew experienced the accident somewhat differently. The two occupants stated that they had set the aircraft down in front of the hangar after the hover. The flight instructor had even already noted the landing time when suddenly there was a thud and the machine was thrown from one runner to the other several times. Then the pilots noticed that the helicopter was starting to burn and fled the cockpit.

The two crew members get off lightly, but the material damage is enormous: the four-seater helicopter is completely destroyed by the fire. In addition, the flying parts of the machine damage not only the hall gate, but also another helicopter parked in the hall.

R44: The four-seat helicopter is completely destroyed by the fire

The investigation of the accident is not easy for the investigators of the Federal Aircraft Accident Investigation (BFU) because of the differing statements. A few indications at the scene of the accident speak in favor of the eyewitness version. The hall gate, in front of which the helicopter got out of control, was broken through in several places - probably by the rotor blades of the R44. The trail of the impacts gradually descends from a height of four meters.

However, the R44 is only 3.28 meters high: This could indicate that the helicopter was actually still in hover when the rotor hit the hall gate. Then a pilot error would probably be the cause of the collision. However, the crew was also able to put forward some arguments for their version, in which the helicopter had already been on the ground at the time of the collision. An attempt to explain: The rotor touches the hall door and splinters, parts flying around cause the upper holes.

No hovering

The so-called cone angle could also explain the upper holes in the hall door: the rotor blades bend upwards due to the lift, so their tips rotate above the rotor head. This can be observed particularly with heavy machines and high g-forces. However, the Robinson R44 is classified as a light helicopter, and even with the engine running, there are no increased g-forces on the ground. The cause of the accident remains officially unclear for the BFU. What is certain, however, in all suspicions is that the pilots should not have been allowed to float in front of the hall gate; Such a maneuver is simply forbidden in the user regulations of the Straubing-Wallmühle airfield. For good reason, as the accident shows.

The Aviation Office of Southern Bavaria has now issued a decision that has once again generally prohibited hovering flights, take-offs and landings between buildings. A minimum distance of three rotor diameters must be maintained between obstacles. There are just 20 meters between the halls in Straubing, but the rotor of the R44 has a diameter of 10.06 meters. After all - the helicopter's fire could perhaps have been avoided if the retrofitting with a safety tank required by the manufacturer had already been carried out. The owner had until the end of 2014 to do this. Without this tank, however, the R44 carries the increased risk of losing fuel and catching fire in the event of an accident.

Text: Samuel Pichlmaier, aviator magazine 10/2011