Sunday, July 1, 2007
Flight Training Tips: Dancing With the Devil
If you are working as a helicopter pilot, you are likely doing recurrent training on emergency procedures once or twice each year. That means this type of accident could happen to you. If you are a certificated flight instructor (CFI), you are even more likely to be involved in one. Also, you ultimately will be responsible for what the pilot does during autorotation training.
Most autorotation accidents can be prevented by both the pilot and the CFI following a few simple steps. First, maintain clear communication with each other regarding all maneuvers to be performed. Second, ensure that airspeed, rotor rpm, and rate of descent are stabilized before completing the autorotations. Third, identify a safe touchdown point to use should mechanical or other problems occur.
A review of the U.S. National Transportation Safety Board’s aviation accident database offers some training insight on this issue. Several of my conclusions here are based on the manner in which the facts are presented in the database. Please keep in mind that the information in the database is limited information and may not contain all of the pertinent facts of an incident. Also keep in mind that these incident reviews and conclusions are for the purpose of educating other pilots and CFIs, and are not intended to criticize anyone.
Before we explore some possible solutions to the problems encountered during autorotation training, an overview of the NTSB accident reports will give us a perspective of the problem. The database listed 195 helicopter accidents during 2006, and 15 of those occurred during autorotation practice (which is 7.7 percent of the total accidents). Of the 15, 10 occurred in piston helicopters (three Robinson Helicopter R22s, six Schweizer Aircraft 269Cs, one Hughes 269A). The remaining five occurred in turbine helicopters.
None of the accidents were fatal.
The majority occurred in piston helicopters during what may have been initial helicopter instruction with inexperienced pilots. However, many of those in turbine helicopters had similar causes. Furthermore, most of the turbine accidents occurred while pilots with at least a commercial rating were performing the practice autorotations. It is clear from this overview that the situations that lead to autorotation accidents affect pilots of all certification levels.
Communication is Key
Communication between the CFI and pilot is critical, especially when conducting autorotation training. Communication begins on the ground when the training flight is being planned. The CFI should describe the maneuvers to be performed, and the pilot being evaluated should have a clear picture of what to expect during the training session. Though some CFIs might believe that the pilot should be ready to respond to any problem at any time, initiating a simulated emergency without any warning is just asking for trouble. The setup for each maneuver should also be discussed, and any commands to be used should be understood by both parties prior to the training session. Any surprises during the training flight may cause miscues that could result in an accident.
During 2006, the NTSB reported two hovering autorotation accidents that may have been influenced by poor communication. In both situations, CFIs initiated hovering autorotations during either preparation for takeoff or when preparing to park the aircraft. The response of the pilots in each circumstance was improper or excessive control input. One pilot lowered the collective when the maneuver was initiated, and the other applied excessive forward cyclic and immediately pulled up on the collective. A complete review of the maneuver and clear communication of expectations might have prevented these accidents.
In another accident, a commercial pilot was performing an autorotation with a power recovery in a turbine helicopter as part of a CFI check ride with an FAA examiner. When the recovery did not appear to be going well (because the pilot failed to roll on sufficient throttle prior to the flare), the examiner said, "Power, power, power." The examiner wanted the pilot to roll on the throttle, but the pilot interpreted this as "Pull collective." This confusion created a situation that left very little collective to cushion the touchdown, resulting in an accident.
Since the FAA examiner was conducting a check ride, the miscommunication became the responsibility of the commercial pilot, who wrecked the helicopter and failed the check ride.
In addition to communication issues raised by this incident, it should be standard practice for turbine helicopter pilots to roll on the throttle well before the flare to prevent timing or coordination problems during the most critical part of the autorotation.
Since so much is riding on the proper completion of a practice autorotation, CFIs must ensure that the maneuver is conducted safely. Several years ago, Robinson came out with a safety notice for conducting safe practice autorotations. Though it was specific to Robinson, the concepts are applicable to all practice autorotations: airspeed, rotor rpm and rate of descent must be stabilized before the helicopter is 100 ft agl.
If these conditions are not met, the practice autorotation should be aborted and a go-around initiated. Though most pilots would prefer not to admit that their maneuver needs improvement, initiating a go-around can be the difference between dented pride and a dented helicopter.
One accident that occurred in an R22 was the result of the instructor allowing an excessive rate of descent. Though the instructor initiated a go-around, it was too late and a hard landing resulted. A similar accident occurred when an experienced instructor was conducting simulated forced landings in a Schweizer 269C. The rotor rpm decayed and the helicopter developed a high sink rate. Attempts to regain rotor rpm were unsuccessful and the helicopter landed hard and rolled over on its side. In another accident involving a high-time CFI flying with a high-time, air transport pilot-rated student, a Bell 206L-4 experienced a hard landing as a result of low rotor rpm during touchdown.
These accidents occurred in different types of aircraft with pilots of various levels of experience. However, the causes are similar. Clues that trends in airspeed, rotor rpm, and airspeed are developing should be closely monitored and handled well before the 100-ft agl mark. Distractions in the cockpit or focusing too much on one indicator can make a bad situation worse, so early detection of trends is critical during practice autorotations.
Identify a Touchdown Point
Three autorotation accidents that occurred when the engine failed after the maneuver was initiated remind us that it is essential to have a safe touchdown area identified in case a full-touchdown autorotation is necessary.
Other authors have already addressed the point that autorotations should be conducted to a runway or taxiway and not the grass. The reason that practice autorotations should be conducted to the pavement is that the grass does not allow the skids to flex and absorb energy as they were designed to do. Also, it is difficult to get a skid stuck in the asphalt if there is any bounce or a nose-low attitude. Grassy areas can easily catch a skid and turn a messy touchdown into a dynamic rollover.
All three of the autorotation accidents that followed engine failure during entry occurred in the Schweizer 269C or Hughes 269A.
One happened over an open field that was not level. Upon touchdown, the helicopter rolled over to the right. In another, a grass field with a slight upslope was the touchdown location. The helicopter slid backward down the slope, causing the tail boom to flex up and make contact with the main rotor. Both of these incidents might be been prevented had the practice autorotation been conducted to a paved surface.
In another incident (which did not involve an engine failure) a 180-deg. full touchdown autorotation was conducted to the grass. The pilot leveled the aircraft and assumed a slight nose-low attitude, which caused a bounce and a yaw to the left. The helicopter contacted the ground with right sideward momentum and a skid dug into the grass, causing the helicopter to roll over. The pilot’s cyclic input caused problems with the touchdown portion of the recovery phase, but the grass surface clearly added to the problem.
Practice autorotations are similar to firearms training for law enforcement officers. Pilots spend a lot of time preparing for a situation that they will likely never encounter during their flying careers.
Each year, there are very few mechanical failures that require the use of emergency procedures to safely land a helicopter. Due to the risk involved, both to pilot careers and personal safety, it is imperative that pilots and CFIs clearly communicate, stabilize cockpit indications, and identify a safe touchdown zone when conducting practice autorotations.
Unlike a bullet fired from a gun, a poorly executed autorotation can be turned into a go-around and attempted again.