Sunday, April 1, 2007
Safety Watch: Understanding a Student's Background
ACCORDING TO THE U.S. NATIONAL Transportation Safety Board, on May 28, 2005, about 1150 Pacific Daylight Time, a Robinson R44 impacted terrain while maneuvering during low-level flight near Lucerne Valley, Calif. The owner, a private pilot, was seriously injured, as was a safety pilot (who was also a CFI) and one passenger. The helicopter was destroyed following a post-impact fire.
A witness reported that, shortly after crossing the racecourse southbound at a low altitude, it appeared that the helicopter was attempting to reverse course back toward the north. The helicopter pitched nose down and leveled off just before it impacted a dry streambed. Upon impact, the helicopter burst into flames. All three people on board sustained burns while exiting the burning helicopter.
During an NTSB interview on June 15, 2005, the CFI reported he was the safety pilot for the flight and not pilot-in-command, and they had been flying for about 1 hr on the photo flight when the accident occurred. While southbound and crossing the racecourse, the private pilot started to turn the helicopter to the right when the helicopter began spinning to the right.
The CFI said the private pilot told him he had lost control and asked for help. The CFI took over the flight controls, and tried to keep the helicopter in a level attitude. The helicopter was descending, and the CFI realized the rotor rpm was decaying. He knew he was too low to try to recover the rpm, so he tried to cushion the impact with the collective. The helicopter impacted the ground and rolled onto its left side. Prior to the accident, the CFI thought the helicopter had been operating normally.
The NTSB interviewed the private pilot on Aug. 4, 2005 and he also stated he was flying southbound along the racecourse, then made a hard right, 180-deg turn and lost control of the helicopter. The CFI took the controls and tried to recover. The pilot stated the helicopter and engine had no mechanical failures or malfunctions during the flight.
The private pilot indicated he used to fly off road races in his airplane and this was his second flight using a helicopter. He added the accident flight was the first time he had flown this type of operation with his own helicopter and as pilot-in-command. The pilot had just completed the Robinson Helicopter safety course, but he stated he did not know about Robinson Safety Notice SN-34, which cautions inexperienced helicopter pilots about flying photo flights.
A review of FAA airman records revealed the pilot held a private pilot certificate with ratings for airplane single-engine land and multi-engine land. An additional rating for rotorcraft-helicopter was added seven days prior to the accident. At that time, the pilot reported a total airplane time of 1,550 hr and total helicopter time of 50 hr.
At the time of the accident, the CFI estimated the pilot had about 70 hr of helicopter flight time. The CFI held a commercial pilot certificate with a rating for rotorcraft-helicopter and a certified flight instructor rating for rotorcraft-helicopter. According to the CFI, he had 520 hr total flight time in rotorcraft, including 130 hr of flight instruction given in rotorcraft. The CFI had received his endorsement for the R44 seven days before the accident.
The calculated gross weight at the time of the accident was 180 lb below the max gross weight of 2,400 lb. The accident site was located at 4,266 ft msl and the temperature was about 90F, creating a density altitude of 7,350 ft.
Robinson issued Safety Notice SN-34 in March 1999, titled "Photo Flights - Very High Risk." It describes the problems encountered when the pilot slows the helicopter below 30 KIAS and then attempts to maneuver the helicopter.
"The helicopter can rapidly lose transitional lift and begin to settle," it states. "An inexperienced pilot may raise the collective to stop the descent. This can reduce rpm, thereby reducing power available and causing an even greater descent rate and further loss of rpm.
"Because tail rotor thrust is proportional to the square of rpm, if the rpm drops below 80 percent nearly half of the tail rotor thrust is lost and the helicopter will rotate nose over. Suddenly, the decreasing rpm also causes the main rotor to stall and the helicopter falls rapidly while continuing to rotate." The safety notice recommends photo flights only be conducted by well-trained, experienced pilots.
Robinson also addresses the problems with experienced fixed-wing pilots transitioning to helicopters in Safety Notice SN-29. It states that the ingrained reactions of an experienced airplane pilot can be deadly when flying a helicopter. It cites an example of the airplane pilot’s sudden response to a stall-like warning horn being to push the stick forward and add power. If a pilot were reacting this way to a similar sounding low-rotor horn, it would drive the rpm even lower and could result in rotor stall.
This accident underscores the importance of CFIs understanding the background and experience level of their student.
Tim McAdams has more than 9,000 total flight hours, with 7,000 in helicopters. A helicopter CFI and a fixed- and rotor-wing ATP, he flies a single-pilot IFR Agusta 109E for CareFlite in Dallas. You can reach him at firstname.lastname@example.org.