Archive for August, 2012

Wire strikes

Friday, August 24th, 2012

Some of the advantages of helicopters are the ability to fly very slow and land in small unapproved areas. As such, they perform many jobs that increase the risk of hitting a wire. Wire strikes have happened in just about all segments of the helicopter industry.

EMS pilots landing on roads and fields have to be extremely careful, especially at night or during the day when bright sunlight produces glare. Small power lines crossing roads and fields can be very difficult to see and several accidents have occurred when a departing helicopter contacts a wire. If a helicopter is heavily loaded and has little power available the pilot needs to gain airspeed to increase lift for climb out. This raises the risk of hitting an unseen wire. Just such an accident happened earlier this year in Tennessee (NTSB Identification: ERA11IA436). If power is available, a max performance or straight-up climb can mitigate the risk of an accident. I believe NTSB data shows the probability of an engine failure is smaller than the probability of hitting a wire or obstruction.

Even pilots who operate around power lines routinely must be alert. In July of 2011 a pilot flying an aerial application flight contacted a power line that ran perpendicular to the direction of the spray run. The pilot told the NTSB he was aware of the power line, but became distracted by horses that were located near the field. Moreover, during an aerial power line observation flight, the pilot hit the static wire for the power line he was patrolling. The pilot reported to the NTSB that he never lost control of the helicopter, but landed as soon as he could in a parking lot close to where the wire strike occurred. In this case, the helicopter was equipped with wire strike protection and a 12 inch piece of the 7-strand wire was found in the wire cutter located below the main rotor mast.

Robinson Helicopter has identified wire strikes as the number one cause of fatal accidents in helicopters. The company has published a safety notice (SN-16) that provides advice like crossing power lines at the support towers, being aware of the smaller grounding wires and flying at least 500 feet AGL whenever possible.

Helicopter dollies

Tuesday, August 7th, 2012

Although some helicopters have wheels, most have skid type landing gear. One of the biggest problems with skids is how to easily move the helicopter around on the ground. Attaching ground handling wheels to the skids is an option that works well for a small helicopter like the Robinson R22. However, for larger turbine helicopters the wheels are bigger and not very convenient to carry with the helicopter. Moreover, it normally requires more than one person to maneuver a heavy helicopter on wheels. As such, the helicopter dolly is a common option.

A helicopter dolly is a wooden, sometimes metal, platform with wheels that a helicopter can land on. Once the helicopter is on the dolly it can be towed with a tractor or tug. Landing on a dolly can be hazardous and there are some pilots that do not think it’s worth the risk. The danger comes from the difficulty seeing the skid gear while having to precisely set the helicopter on the platform. Some dollies do not have a lot of extra room so even a little drift at the last minute can cause one skid to miss the platform and the helicopter to roll over. Even if the pilot realizes this and attempts to abort there is the possibility that the skid will get caught on the edge, also causing a roll over. These types of accidents have all happened. There was even a case where the pilot did a nice dolly landing, rolled the engine to idle and then realized the dolly wheels were not chocked. The dolly started rolling and stopped when the helicopter’s nose hit a parked tug.

The pilots that support dolly landings say that with the proper mindset and approach, dolly landings are safe. For example, taking your time with the set down, not being nervous and getting instruction. Additionally, the dolly should be into the wind and large enough to accommodate the helicopter while allowing room for error.