Confined area operations

June 22, 2011 by Tim McAdams

The very nature of helicopters, especially in EMS operations, requires maneuvering in close proximity to objects. Large solid objects like walls and fences can create very turbulent air by interfering with a normal rotor downwash pattern. In a hover near the ground, the air being accelerated down hits the ground and travels away from the helicopter. When this air encounters a large solid object it slows down and gets redirected disrupting the air flow through the rotor system Typically, the side close to the object sees more disturbed air creating a lift imbalance felt by the pilot as pitch and roll instability. Depending on the location of the object relative to the wind (which can hurt or help the situation) the instability can be mild to severe. Turbulent air that gets near the tail rotor can cause yaw instability as well. The constantly changing air flow creates fluctuating lift from the rotor requiring power changes to maintain a hover. For a helicopter that is heavy and operating at a high density altitude, insufficient power available could cause a hard landing.

However, a bigger danger is actually striking the object with the rotor system. According to the NTSB, on Aug. 31, 2002, the pilot in command of a Sikorsky S-76 taking off from a hospital helipad became distracted by a large section of torn awning that was flapping in the wind due to rotor wash. The main rotors struck the top corner of the building and the helicopter began to settle. The pilot lowered the collective and navigated between the building and the parking garage to the street below, applying full collective pitch to help cushion the hard landing. The pilot and two medical crewmembers received minor injuries.

That same year the pilot and flight nurse of a BK117 were not so lucky when their helicopter struck the hospital building at night during gusty wind conditions. The paramedic was the only survivor and said that when the helicopter was about 20 ft. above the helipad, he was programming the GPS receiver and felt a sudden gust of wind push the helicopter from behind. He was not alerted to anything unusual until he looked up and noticed the helicopter’s close proximity to a 16-floor brick building that extended above the height of the helipad by four floors. The paramedic yelled, “Building, building, building!” to alert the pilot, who then made a rapid right cyclic input to avoid hitting the building. But the helicopter struck the building and fell about 13 floors to ground level.

Operating in a confined area during gusty wind conditions requires enhanced concentration especially during operations at high density altitudes.

6 Responses to “Confined area operations”

  1. pdxpilot Says:

    Good points to keep in mind – always something to think about when flying a helicopter. Not like having a plane at 5,000 feet in trim so you can fly hands off.

  2. sean c Says:

    There is no excuse for trying to do anything else but fly the aircraft when you are taking off or landing to a confined area. Any programming of avionics or any other action that takes your eyes off the obstacles, especially at a hover, is unacceptable. That kind of thing must be done either on the ground prior to takeoff, or in cruise flight at altitude. If something comes up unexpectedly at the moment that you are lifting off to hover and you have to re-enter a change of destination, either start off in that general direction and do it in cruise, or set it back down and do it on the ground. The extra couple of minutes it takes are inconsequential.

    Multi-tasking is fine and good, as long as you are NOT hovering the aircraft into or out of a clearing or confined helipad at the time. The work load and the consequences are just too high in this situation, and flying the aircraft must always remain the SOLE task during this critical phase of flight.

  3. Dr. John Says:

    Tim: Excellent point. Objects disrupting smooth air dispersal, wind gusts or other sudden issues can cause serious non recoverable circumstances. Unplanned or unexpected issues are scary but there are things we can do to minimize the net results. We can’t change the laws of physics but we can do our very best to handle a threatening situation. Most fixed wing pilots forget the source of lift to a rotary system is greatly different than fixed wing. Close quarters only complicates that. I’ve seen some good maneuvers from very seasoned rotary pilots who deserve a serious attaboy or visit to the local therapist for even flying on of these concoctions. But, oh how we love ‘em! Thanks.
    John.

  4. grumpy Says:

    The way I read the article, it was the paramedic, not the pilot, who was programing the GPS prior to the crash.

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