Wind

April 12, 2010 by Tim McAdams

 To a helicopter pilot, a brisk wind can provide a nice performance boost. However, gusty winds can sometimes be tricky to manage. According to the NTSB, during the last 10 years there were 48 helicopter accidents in which the pilot said a gust of wind was a factor.

On March 27, 2002, a student and instructor were hovering a Hughes 269 helicopter (a small two-seat piston powered trainer) at the Fort Collins Downtown Airport in Colorado. The instructor pilot reported that the wind was 2 or 3 knots at takeoff, but forecast to be gusty in the afternoon. While hovering at about 3 ft, with the student pilot at the controls, the helicopter encountered a very strong gust and began to wobble. The instructor took control of the helicopter and climbed to about 15 feet. Then another gust hit the helicopter, turning it sideways and then downwind. The instructor stated he was attempting to get it on the ground, but the wind continued to drive the helicopter forward with excessive nose-over tendency.

With the tail rotor into the wind, creating a high power demand and limited tail-rotor authority, the helicopter skipped along the dirt two or three times traveling about 200 feet. The right strut failed, and the helicopter rolled over on its right side.

Ten minutes after the accident the reported weather at the Fort Collins-Loveland Municipal Airport, 8 nm south of the accident site, was wind from 260 degrees at 13 knots, gusting to 25.

It is not surprising that many accidents were reported while hovering with students. However, like the following, some happened while in flight.

On June 12, 1997, the pilot of a Bell 206L-3 was flying his fourth trip of the day over a proposed gas pipeline route 15 miles southwest of Weston, Colorado. The flight was for the purpose of conducting a bird study and required low and slow flight over wooded areas.

The pilot said he crested a ridge and descended into the next valley, following the terrain downhill. As he approached the far side of the valley, he stated he was going to need a climbing 360-degree turn to clear the next ridge. After completing about 90 degrees of the turn the helicopter was hit by a gust from the rear, causing a significant decrease in airspeed. The pilot said he had to decide whether to attempt to complete the turn and risk striking a tree with forward speed, or try a landing with zero airspeed. He chose the latter. The helicopter settled into trees and rolled over on its right side. The commercial pilot and four passengers escaped injury.

Reported winds don’t always tell the complete story. The NTSB report listed winds from 100 degrees at 13 knots. Ridges and valleys can cause different and strange wind patterns. Flying low and slow at high density altitudes and high gross weight can make even a small wind change very demanding.

2 Responses to “Wind”

  1. Chris Says:

    In the first report, was there any indication that the wind was going to pick up so suddenly (like an approaching storm or lighter gusts leading up to this 13/25 gust)? What could the instructor have done to have prevented the crash? What can we learn from this report?

  2. Ehud Gavron Says:

    In the first story…

    As students we were taught to hover at the 5ft level — 3 is way too close to the ground for an unskilled pilot. I tend to do 2ft hovers in calm weather and familiar equipment for the simple reason that at 6000ft density altitude, a hover auto works better from there. (R44/R22, Tucson AZ 85F 2640MSL).

    Secondly the instructor’s instinct to climb was good but he should have turned it into the wind, thereby making the rotor system efficient (and with 13-25 he’d be at ETL already).

    Finally once he realized his control was slipping he should have started forward motion… any forward motion. A helicopter’s control surfaces work much better with high speed air.

    In the 206, the pilot misjudged the required altitude, and so did the last minute tight 360 that he did not complete. Had he been maintaining reasonable altitude over terrain, or extended the 360 out, likely he would have been fine.

    There’s a tendency which they call “get-there-itis” but also applies to “Hey I’m right here at the ridgline… oh damn. Well I can fix this without going out of my way…” and this is what happens. The “right” ego-free reaction is “I’m not high enough, let me get away from terrain and climb.”

    I’d love to hear other people’s opinions :) (or tell me if my suggestions are wrong :)

    Ehud

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