One of the topics discussed in all police training courses is “command presence.” This is all about being able to communicate your wishes to another with both courtesy and authority in a manner to guarantee the desired compliance. Perhaps command presence training could serve business pilots as well. Sometimes to perform your duty to operate a flight safely, you must exercise command presence — telling the boss “No” or, perhaps, insisting on an alternative course of action.
I suspect most helicopter pilots are familiar with the accident investigation we will explore this month. But there are lessons here for fixed-wing pilots as well. The investigation took almost three years to complete, but the conclusions were surprising, to say the least.
About 1500 on Feb. 14, 2010, numerous people in and around Cave Creek, Ariz. — a Scottsdale exurb — heard a series of noises they later described as “bangs” or “pops.” All looked up and saw parts fly from aEC135 T1 twin-turbine helicopter and then watched as the machine nosed down, fell 2,000 ft. and crashed into open terrain. The wreckage ended up just north of a river wash on a residential gravel access road about 14 nm north of Scottsdale Airport at an elevation of 2,356 ft. MSL.
First responders arrived minutes later. Within moments of their arrival, however, fire erupted and intensified, consuming the wreckage. Ultimately emergency workers recovered the bodies of four adults, one child and two dogs from the wreckage. All were dead at the scene. The accident was not survivable.
The helicopter was registered to a Scottsdale company and was operated under FAR Part 91 as a personal cross-country machine. VMC prevailed at the time of the accident and no flight plan had been filed. The flight departed the Whispering Pines Ranch in Parks, Ariz., at about 1430 destined for Scottsdale Airport (SDL).
Employees of the owner told investigators that the helicopter made frequent trips between SDL and the Whispering Pines Ranch. It had arrived at the ranch on Feb. 12. On the morning of the accident, the pilot, the owner and three other passengers, along with the dogs, arrived at the helicopter hangar. The ranch foreman placed the passengers' personal items on the ground outside of the baggage compartment at the rear and the pilot placed the items in the aircraft as was his custom.
The foreman observed the pilot complete a preflight inspection, enter the cockpit and sit in the right front seat and start the engines. The foreman assisted an adult female into the rear cabin area where she occupied the left rear aft-facing seat. A male passenger boarded the helicopter and sat in the right rear forward-facing seat. The foreman then loaded a small dog in the left rear forward-facing seat directly across from the woman and a larger dog that was positioned on the floor between the left rear aft-facing and forward-facing seats. The foreman closed the right passenger door and ensured that it was locked.
Next, the foreman moved to the right front pilot's position. He saw the helicopter owner, a fixed-wing pilot, and his five-year-old, 42-lb. daughter walk around in front of the aircraft and board from the left forward cockpit door where they both occupied the left front cockpit seat, with the small girl positioned on her father's lap. The foreman told investigators that the owner “occasionally” allowed his daughter to ride in his lap in the right seat. For this flight he said he was unsure if either the owner or the child were secured, but on previous flights, the man had strapped his daughter on top of himself.
After everyone was on board, the foreman closed the right passenger door and ensured that it was locked and secured. He then went forward to the right front cockpit window area, looked at the pilot who had his shoulder harness and seatbelt on, and motioned to him that the right passenger door was secured and the helicopter was ready for departure. The foreman watched the helicopter lift off, ascend to about 100 to 150 ft., make a 180-deg. turn to the north and begin forward flight heading northwest.
Phoenix terminal radar approach control first picked up the helicopter about 11 mi. south of the Whispering Pines Ranch at 1443:30. The aircraft was flying south toward SDL at a Mode C reported altitude of 7,500 ft. MSL and remained at that altitude until 1451:16, when it initiated a gradual descent that lasted until 1457:41. The helicopter was then at 6,000 ft. MSL. From this point, the helicopter initially climbed and then began a gradual descent with slight altitude, heading and airspeed fluctuations until 1503:27, when it reached 4,400 ft. MSL.
Radar data then depicted the helicopter make a rapid (5 sec.) climb from 4,400 ft. to 4,700 ft. followed by a rapid descent to 3,800 ft. MSL within the next 5 sec. The last radar return was recorded at 1503:37.
At the same time, several ground witnesses looked skyward when they heard a series of “pops” or “bangs.” They saw parts flying from the helicopter and watched as it spiraled into the ground.
Investigators from the, , American Eurocopter and USA began operations the next morning. On Feb. 18, they were joined by representatives of the German Federal Bureau of Aircraft Accident Investigation (BFU) and Eurocopter Deutschland.
The linear debris path — consisting primarily of pieces of yellow main rotor blade and the left horizontal endplate — extended north from the main wreckage about 2,000 ft. All major aircraft components were accounted for near the wreckage or along the flightpath. There was no evidence of an inflight fire.
Impact forces and the post-crash fire destroyed the cockpit and cabin areas. The cockpit floor structure exhibited accordion compression in the aft direction. The twist grip throttles were both found past the neutral detent and in the high range. The anti-torque pedals were found in the near-neutral position. All flight controls were accounted for, and all flight control tube fractures appeared angular and consistent with overload. Those flight control components not damaged by impact forces were found attached and secured. The airspeed indicator had frozen at 103 kt., the rotor rpm gauge indicated 95%, the engine No. 1 gauge indicated 92%, and the engine No. 2 gauge indicated 90%.
The first identified piece of debris along the flightpath leading to the wreckage site was a piece of ribbon from the helicopter's left vertical endplate. An area of main rotor blade debris that included foam, honeycomb and paint chips was then identified extending from the initial point of the debris field south for about 1,050 ft. A large piece of the yellow main rotor blade was located about 750 ft. north of the main wreckage site. A fragment of the helicopter's tail-rotor driveshaft flex coupling was found about 695 ft. north of the wreckage. A lower piece of the left vertical fin was located about 450 ft. north of the main wreckage.
A further survey of the area revealed that a piece of the yellow blade tip was found about 400 ft. northwest of the main wreckage, with myriad small fragmented pieces of the helicopter observed between the blade tip and the wreckage site. The main rotor blades and hub were located about 25 ft. north of the primary wreckage site. The tail boom fenestron was lying on its right side at the main wreckage site and oriented in a north-to-south direction. Its ring frame exhibited heat damage and the fracture surfaces were consistent with overload.
No obvious preimpact mechanical anomalies were observed on any of the hydraulic system components. All main transmission gear/component damage was consistent with impact and/or overload. The main transmission anti-resonance isolation system mounts were examined on site, with no evidence of preimpact damage. The damage to the main transmission torque strut was consistent with impact and overload.
The engines were removed for detailed study. No evidence of preimpact failure was observed. In addition, the helicopter's gross weight fell within the flight envelope and below the helicopter's maximum certified gross weight at the time of the accident.
In the end, it seemed clear that the main rotor disc had moved from its normal plane, allowing the yellow blade to strike the tail.
Main Rotor Disc Divergence From Normal Plane of Rotation
Eurocopter conducted a study to determine what condition or event could have caused the main rotor disc to divert from its normal plane of rotation and strike the endplates and the tail-rotor driveshaft. The study started with an assumption that contact between the main rotor blades and the endplates or tail boom could only be possible when a pilot carries out an extreme aft cyclic input.
Eurocopter initially studied the possibility of an occurrence termed as an “Aggressive Pull Aft” maneuver during fast forward flight, where the pilot aggressively pulls the cyclic pitch from a forward position fully to the aft stop. In a simulation model, it was demonstrated that during an “Aggressive Pull Aft” maneuver alone, sufficient clearance to the endplates and tail boom existed. As a result, Eurocopter concluded that another flight maneuver must precede the “Aggressive Pull Aft” to explain the excessive flapping required that would result in the main rotor blade collision with the endplates and the tail boom.
To address this issue and through approved engineering and simulation models, Eurocopter provided the investigation team with two accident flight maneuver sequence scenarios. In each case, the maneuver sequence starts at the same cruise flight condition (fast, forward flight, high collective pitch and forward longitudinal cyclic).
Scenario No. 1: Push cyclic full remaining range forward and then pull full range of longitudinal cyclic control backward (cyclic push/pull maneuver). Eurocopter determined that the control sequence in scenario No. 1 resulted in an increased blade deflection when compared to the “Aggressive Pull Aft” maneuver but still showed enough clearance between the main rotor disc and the tail section of the helicopter.
Scenario No. 2: Sudden lowering of the collective to near the lower stop, followed by a simultaneous reaction of nearly full up collective and nearly full-aft cyclic (longitudinal).
“Eurocopter determined that the control sequence in scenario No. 2, based on known conditions at the time of the accident and the laws of physics and aerodynamic principles, was the only maneuver that would result in main rotor blade contact with the endplates and tail boom,” said investigators.
Members of the investigation team, which included the NTSB chief scientist, an NTSB structures engineer, an NTSB materials engineer, a BFU accredited representative and a representative from the FAA's Rotorcraft Directorate, conducted a thorough review of Eurocopter's study and concurred with the findings of the study as presented.
The 63-year-old PIC held a commercial pilot certificate for rotorcraft-helicopter, had a valid second-class medical and had accumulated over 11,000 hr. flight time, 824 hr. of that in the EC135 T1. He had flown 13 hr. in the preceding 90 days. All ground and flight training records indicate satisfactory performance with no deficiencies noted. However, two American Eurocopter instructor pilots who had provided the pilot with EC135 T1 instruction from 2002 through 2008 told the NTSB of concerns they had with statements the accident pilot had made during training.
The first instructor pilot provided the accident pilot with his initial transition ground school training in 2002, followed by recurrent training in 2003, 2004 and 2006. The instructor pilot reported that during his training in 2002, the accident pilot displayed an abnormally high degree of pressure to accomplish flights from the helicopter's owner and that he was visibly shaken when discussing the amount of pressure he received.
The instructor stated that during the week he spent training the accident pilot, the conversation regarding his employer often turned to the difficulties he endured to keep flights on schedule.
The instructor revealed that the accident pilot stated that it would not be uncommon to fly the helicopter's owner from Seattle to his home on Vashon Island, Wash., when the weather conditions at night were so poor that they would follow the ferryboat lights to navigate across the bay under foggy conditions.
The first instructor pilot also reported that in 2004 he provided the accident pilot recurrent training after an incident that damaged the helicopter. He told investigators that the accident pilot stated that he was to fly to Vashon Island to pick up the owner's wife to fly her to the Seattle airport. After landing on the island, the accident pilot left the helicopter's engines running and the controls locked while he loaded the passengers and bags. When he attempted takeoff, the cyclic control lock was still engaged, which resulted in damage to the tail boom following the attempted landing. The instructor pilot added that the accident pilot admitted to him that he was flustered because he had to hurry and depart as soon as possible.
The second instructor pilot, who provided instruction to the accident pilot during summer 2008, stated that he remembered the pilot commenting about how the helicopter's owner dominated the cockpit duties before a flight. The accident pilot revealed that when the owner flew (even though he was not rotary-wing rated), he would get in the cockpit, flip switches and go. The instructor reported that he felt that the accident pilot was intimidated by the owner and would not insist that proper aircraft procedures be followed.
In a submission to investigators, the chief pilot for flight operations at the owner's company characterized the accident pilot as a Vietnam-era combat pilot who had also flown for the U.S. Forest Service in the Pacific Northwest, a very demanding region of the U.S. in which to fly. Additionally, he characterized the accident pilot as a conscientious and professional pilot in every sense of the word, and a person who would not be intimidated.
The Owner (Fixed-Wing) Pilot
The owner-pilot was 64 years old. He sat in the right seat with his daughter on his lap. He possessed a private pilot certificate for airplane single-engine land issued in 1967. Investigators could find no recent medical certificate. Additionally, the investigation failed to reveal any information about the owner-pilot's training or total flight hours. Certainly, he was not rated to fly helicopters. When asked if the owner ever flew the helicopter, the chief pilot responded that it was common for him to fly and that, “He liked to fly.”
So What Happened?
The investigation focused on the controls. All agreed that the experienced PIC would never have slammed the collective down, jerked it back up and pulled the cyclic full aft. So had that control manipulation sequence led to the accident?
The investigators conducted a biomechanical study and determined that it was feasible that the child sitting on the owner's lap in the left front cockpit seat could fully depress the left-side collective control by stepping on it with her left foot. The collective has a breakout force of between 2.2 and 3.1 lb. and would only need a maximum force of 5 lb. to move the control fully. Thus, the force to displace the collective fully was a maximum of 8.1 lb., which is much less than the child's total weight and less than she would exert with her left foot if pushing to stand up from a seated position.
The study also found that the collective lever's full range of motion was 9.5 in. from full up to full down and that the spacing between the left edge of the seat, the collective and the door are sufficient for the child's foot to rest on the collective and depress it. The study noted that the cyclic control could be moved to the full-aft position even with a small child of this size sitting on her father's lap in various positions.
Because the spacing between the upper partition, which separated the cockpit from the aft cabin compartment, and the ceiling was about 5 in., it is unlikely that the child could shift from the left front cockpit seat to one of the rear seats during the flight. Considering that the child was sitting on the owner's lap in the left front cockpit seat, “it is highly likely that the child inadvertently stepped on the collective with her left foot and displaced it to the full down position,” said the Safety Board. This condition would have then resulted in either the pilot or the helicopter owner raising the collective, followed by a full-aft input pull of the cyclic control and the subsequent main rotor departing the normal plane of rotation and striking the left endplate and the aft end of the tail-rotor driveshaft.
During its investigation of this accident, the NTSB found that the PIC was involved in two incidents while operating the accident helicopter; neither incident was reported to the FAA. On May 8, 2003, the helicopter owner was operating the aircraft, and his seat slid aft while on final approach to landing. The helicopter dropped about 50 ft. before impacting terrain, resulting in damage to the horizontal stabilizer. In this incident, the PIC failed to use proper cockpit discipline when he allowed the helicopter owner to operate the helicopter's controls, particularly during a critical phase of flight.
Although it could not be determined who was flying the helicopter at the time of the accident (and it is not relevant to the cause of this accident), the previous incidents, the statement by the pilot that the helicopter owner dominated cockpit duties, and the PIC allowing the owner's daughter to sit on his lap during flight together indicate that the PIC did not maintain strong cockpit discipline.
The Safety Board determined the probable cause(s) of the fatal accident to be: “The sudden and inadvertent lowering of the collective to near the lower stop, followed by a simultaneous movement of the collective back up and the cyclic control to a nearly full-aft position, which resulted in the main rotor disc diverging from its normal plane of rotation and striking the tail-rotor driveshaft and culminated in a loss of control and subsequent impact with terrain. Contributing to the accident was absence of proper cockpit discipline from the pilot.”
So, the take-home in this story, it would seem, is that pilots need the command presence to be able to say “No” effectively: “No” to unreasonable operational requests; “No” to untrained owners who want to manipulate the controls in critical, non-training environments; “No” to rushed operations that force the crew to ignore SOPs and widely understood best practices.