On July 2, 1993, a Bell 47G2-M (registration N2473B) was involved in an aviation accident near S. SN Francisco, CA. Investigators recorded the probable cause as: THE PILOT'S INADEQUATE PREFLIGHT PLANNING/PREPARATION WHICH RESULTED IN FLIGHT INTO HIGH WINDS, TURBULENCE AND WINDSHEAR. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter returning from a local photo flight pitched up and nosed over into impact, a sequence characteristic of retreating blade stall, as variable 50 mph winds and severe wind shear affected operations at San Francisco International Airport.
Accident Sequence
A helicopter was returning from a local area photo flight when witnesses observed it pitch up and then nose over into the ground. The sequence of events was characteristic of a retreating blade stall.
Witness Reports
Witnesses reported that the helicopter pitched up and subsequently nosed over to impact. No further details about the witnesses' observations were provided.
Wind Conditions
The prevailing wind at the time was reported to be extremely variable at about 50 miles per hour. The wind conditions were associated with severe wind shear.
Airport Operations
Between 1530 and 1630, 25 airplanes, mostly large airline transport category aircraft, executed missed approaches at San Francisco International Airport (SFO) due to the severe wind shear conditions. The helicopter accident occurred in the same timeframe and vicinity.