NTSB Factual Report

On November 29, 2003, approximately 0250 central standard time, a MBB BK 117 B-2 twin-engine helicopter, N440HH, sustained substantial damage when the tail rotor blades impacted trees while maneuvering near Conroe, Texas. The commercial pilot, flight paramedic, and flight nurse were not injured. The helicopter was registered to and operated by Memorial Hermann Hospital System, Inc., of Houston, Texas. Dark night visual meteorological conditions prevailed, and company flight plan was filed for the 14 Code of Federal Regulations Part 91 positioning flight. The air ambulance flight departed the David Wayne Hooks Memorial Airport, near Houston, Texas, at 0236.

According to the pilot's statement, prior to landing, he performed a "high recon" of the landing zone (LZ). The LZ was marked by four lighted traffic cones, and the wind was from the north. After the on-board medical crew cleared the helicopter from obstacles on the left and right side, the pilot terminated the approach at 200 feet agl. The helicopter was then flown vertically down to the LZ, and at approximately 3-5 feet agl, the pilot initiated a180-degree left pedal turn. Approximately 95-120 degrees into the turn, the pilot heard "what sounded like the rotor's hitting leaves and [tree] limbs." The pilot felt no abnormal vibration with the anti-torque pedals or the helicopter and completed the turn. After landing, the pilot elected not to shut down the helicopter, and inspected the tail rotor. The pilot stated, "Based on the lack of vibration in [the] pedals and airframe, the decision was made not to shut [the aircraft] down and continue the flight back to [the] hospital."

Upon returning to the hospital, the 6,346-hour pilot initiated a post-flight inspection, "paying close attention to the tail rotor." The pilot noted no signs of scratches, dents, or any other types of abnormalities, with the exception of two "small" areas where paint was chipped off. The pilot then contacted the company mechanic on duty, discussed the airworthiness of the aircraft, and "the decision was made, mutually, that the aircraft was airworthy." The flight crew then returned the helicopter to another company facility.

While performing a preflight inspection on the following day, another pilot discovered the damage on the tail rotor blades. He then grounded the aircraft and awaited the arrival of a company mechanic. The pilot reported to operation safety officials that he saw "ripples" in the tail rotor blades paint.

On February 3, 2004, an FAA inspector reported to the NTSB investigator-in-charge that due to the damage sustained, both tail rotor blades were removed and replaced.

NTSB Probable Cause

The pilot's failure to maintain clearance from trees while repositioning in a confined landing zone. Contributing factors were the dark night light conditions and the confined area available to the pilot.