The letter to TOPS urged it to act on the recommendations because of problems it found in investigating the September 20, 2003, crash of Sundance's Aerospatiale AS350BA helicopter. The aircraft slammed into a canyon wall as its pilot maneuvered through Descent Canyon, about 1 1/2 nautical miles east of the Grand Canyon West Airport.

The safety board said passengers interviewed from a previous tour flight, photographic and videotape evidence "indicated that it was not unusual for the accident pilot to fly the helicopter close to canyon walls and at bank angles, pitch attitudes and airspeeds that far exceeded those allowed by company policy, TOPS safety guidelines and some federal regulations."

The company also received at least two written complaints from passengers previously about the pilot but did not discipline him as intended, the NTSB said.

"The safety board determined that the probable cause of this accident was the pilot's disregard of safe flying procedures and misjudgment of the helicopter's proximity to terrain, which resulted in an in-flight collision with a canyon wall," it said.

The FAA's and Sundance's failure "to provide adequate surveillance of Sundance's air tour operations in Descent Canyon" contributed to the accident, it added.

The investigation of the Papillon crash, meanwhile, determined that its "pilot also exhibited unsafe flying practices on previous tours, such as flying the helicopter toward terrain while deliberately keeping his head turned toward the back of the cabin until the passengers screamed for him to turn around," the letter said.

"In addition, the accident site (four miles east of Meadview, Ariz.) was located in an area where the pilot was known to perform high-speed, diving descents during tours to show passengers what it was like to drive a car off a cliff."

The agency's findings "revealed safety issues related to the FAA's surveillance of air tour operations in the Grand Canyon area, the handling of safety-related complaints about tour pilots, the documentation of passenger contact information and operator surveillance of tour routes," it said.