Read More: Identifying Risks in Real Time
February 26, 2019

Don't mistake bad vibrations for business as usual.

There are emergencies … and then there are emergencies. The distinction lies in whether the time frame for responding affords the luxury of, say, consulting a checklist.

In helicopters, many incidents fall into the second class: the pilot’s reaction must be both immediate and exactly correct to avoid balling up the machine. Losses of main rotor rpm (especially in low-inertia systems) or tail rotor control can escalate beyond hope of recovery if those relatively brief sequences of memory items aren’t executed in order and without delay.

Ground resonance is another example. If a fully articulated rotor system becomes unbalanced, the resulting vibration can excite a sympathetic vibration in the airframe. If its frequency is close to the airframe’s natural harmonic frequency, the two vibrations amplify one another until the helicopter shakes itself to pieces. In one famous case in Utah’s Grand Staircase–Escalante National Monument, the aircraft was essentially destroyed within four seconds of the vibration’s onset. The most common cause is a rough touchdown that knocks one blade out of phase with the others, but significant vibration from any cause can have the same effect.

The required response depends on the helicopter’s energy state. If the rotor is still at flying rpm, an immediate lift-off—adding power as necessary—allows the fuselage’s vibrations to dissipate while any out-of-phase blades realign themselves automatically. At low rpm, lowering collective and reducing power to idle may succeed in saving the aircraft. Between those extremes, catastrophic damage is likely, whatever the pilot does—one reason they’re trained to maintain full rotor speed until the helicopter is fully down, settled, and secure.

The Flight

Shortly before 10:00 a.m. on February 15, 2018, an Airbus AS350 B2 landed on the timber pad of a telecommunications tower at Bear Rock, three miles west-northwest of Tulita in Canada’s Northwest Territories. On board were the pilot and one passenger. Photographs taken shortly after the accident show that the pad was mostly clear, with patches of ice covering perhaps 20 percent of its surface. 

The weather was seasonably cold at -27°C (-17°F). With no preheat available on site, the pilot initiated an engine run about 30 minutes after landing in accordance with the AS350 flight manual supplement, Instructions for Operations in Cold Weather. The pilot later acknowledged having noticed some vibration, which he described as “consistent with those felt over the previous three days, both on the ground and during flight.”

At 11:08 a.m. he began a second engine run. Start-up was normal, and the engine accelerated smoothly to 70 percent Ng (gas generator speed). However, when the pilot increased fuel flow to the flight position, the helicopter began to buck fore and aft on its skids.

The pilot reduced fuel flow in response, only to have the bucking intensify, leading him to suspect ground resonance. He increased fuel flow but did not advance it fully or lock it into its flight gate before raising collective, and neither the engine nor main rotor rpm reached their flight-governing ranges before the helicopter lifted from the pad.

The helicopter yawed and drifted to its left as engine rpm spooled up while the main rotor rpm decayed. Two minutes after engine start, the ship descended into the hillside and tumbled down the slope. The pilot—who was wearing his four-point harness but no helmet—managed to extricate himself from the wreckage after the engine shut down. He walked back to the tower’s service building where his passenger administered first aid. 

After the pilot reported the accident, a company helicopter dispatched from Fort Simpson arrived about 3:00 p.m. Both men were initially flown to Yellowknife. The pilot was subsequently airlifted to Edmonton for treatment of injuries including a badly broken arm. Six months later, he was back at work but had not yet returned to flight duty.

The Pilot

The 5,277-hour commercial pilot had 2,017 hours in AS350s, with 6.5 hours in the previous week and 11.7 in the preceding 90 days. He held a Category 1 medical certificate and had completed recurrent training in the AS350 the month before the accident. His age has not been reported.

The Aircraft

The AS350 B2 has a fully articulated, three-bladed main rotor powered by a single 732-horsepower Turbomeca Arriel 1D1 turboshaft engine. Its Starflex rotor head provides full articulation without hinges or lead-lag dampers; instead, flexible thrust bearings at the inboard ends of the mounting sleeves allow the blades to flex, flap, and move in the lead-lag axis, while elastomeric frequency adapters at the sleeves’ outboard ends provide damping. The accident aircraft was manufactured in 1989 and had served for 46,214 cycles comprising 11,005 hours of flight time.

Its landing gear featured two vibration-absorbing systems: flexible steel strips extending downward from the aft ends of the skids, and hydraulic dampers between the front horizontal crosstubes and the fuselage. After the accident, the operator tested the damper assemblies. The right damper (which had seen 1,395 hours of service compared to the left damper’s 3,001) failed the initial functional test, then passed after overhaul. The history of the accident sequence, however, makes it seem unlikely that inadequate damping was a factor.

Four days before the accident, in order to hangar the aircraft overnight, all three main rotor blades had been removed by a technician with the assistance of the same pilot. After they were reinstalled the following morning, the pilot did a ground run and noticed increased vibration.

Although vibration analysis equipment was available at the site, vibration levels were not measured, nor were blade tracking and balance assessed as required by the aircraft’s maintenance manual. Furthermore, the removal and reinstallation of the main rotor blades weren’t recorded in the journey log, contrary to Canadian Aviation Regulations. Investigators learned that the maintenance shop routinely removed and remounted blades without making the required logbook entries.

The vibrations continued throughout the six hours the pilot flew the helicopter during the intervening three days. “During this time,” according to the Transportation Safety Board of Canada’s (TSB) report, “no action was taken to verify or rectify the vibration and no aircraft journey log entries were made.” With no measurements having been recorded, the preaccident tracking and balance status of the rotor could not be determined.

The Response

Following the accident, the operator’s parent company emailed its pilots and maintenance personnel to remind them of the requirement to document all removals and reinstallations of rotor blades in the journey logs. It also instituted an audit procedure to more systematically track those events. Recurrent training for company pilots also stressed the need to record any sudden changes in vibration levels. While the TSB’s report doesn’t state this explicitly, it’s hoped this training also reinforced the importance of investigating and resolving any sudden increases in vibrations before further intensification.

The Takeaway

Professional pilots—particularly those operating in remote locations and extreme environments—can develop a tolerance for apparently benign aircraft anomalies. But discrepancies as seemingly trivial as a burned-out indicator lamp can become the kind of emergency that requires quick recourse to memory items if the wrong thing happens at the wrong time. It’s up to the certificate holder to establish operating procedures, backstopped by applicable national regulations, that remove those decisions and the accompanying temptations from its pilots’ hands. But written procedures count for little if company culture doesn’t identify and call out violations.

Students and low-time pilots might be taken aback by the notion of flying a helicopter that’s had its main rotor blades remounted without first checking blade track and balance. The rotational momentum of all that mass spinning hundreds of times per minute would seem to raise the prospect that any imbalance would quickly build toward catastrophe. But in the field, the need to shelter aircraft from a bitter climate in limited hangar space made this an unremarkable practice—in part, no doubt, due to the lack of adverse consequences up to that time.

In this case, a highly experienced pilot noticed increased levels of vibration without apparently finding them alarming. Over the course of six hours flight in the harsh conditions of a Northwest Territories winter, they presumably did not worsen enough for his survival instincts to command a return to the maintenance hangar. But while pilot-in-command authority should always admit grounding an aircraft in the interest of safety, it’s the operator’s responsibility to identify risks that can’t be left to pilot discretion.

Read More: Lost in Transition
November 14, 2018

Shortcuts in transition training can turn even routine operations into adventures—or tragedies.

“If it’s got wings, I can fly it.”

The phrasing suggests that this attitude is chiefly a fixed-wing problem, but it has parallels in the rotorcraft world. True, airplanes—with their combination of dynamic stability in flight and vastly reduced range of potential landing sites—probably do more to encourage this kind of thinking.

Helicopter pilots may be more apt to recognize the different skills required to go from hovering an R22 to making pinnacle landings in a Chinook (or vice versa), but they can still underestimate the extent of training needed to move between craft of more similar size and power. Thorough transition training imparts the mastery needed to deal promptly and effectively with the unexpected.

While it may be an extreme example, the fatal crash of an Airbus AS350 B3E during an attempted dolly landing in calm weather in Carlsbad, California, shows just how inadequate transition training can severely limit a pilot’s ability to use the aircraft … and to respond to whatever emergencies might arise.

The Flight

N711BE, a 2014-model AStar with just 33 hours on the airframe, took off from Carlsbad shortly after 2:00 p.m. on November 18, 2015. At the controls was the ship’s new owner, a 65-year-old bank president who’d bought the helicopter the previous month. His 60-year-old passenger was also a helicopter pilot, but he had no AS350 experience and only about 180 hours of rotorcraft time overall.

The AStar returned to the airport a little over two hours later and was cleared to land on Runway 24. The pilot descended to the runway at midfield, turned left at Taxiway A3, and then hover-taxied along Taxiway A. The wheeled dolly from which it had departed was at the west end of the Premier Jet FBO (now Atlantic Aviation) ramp, so the pilot approached it from the east, heading directly toward the sun.

His first landing attempt came up short, with the skids roughly centered on the cart’s back edge. The helicopter teetered back until its tail skid hit the ground, then began to rock back and forth, gaining enough force to kick away the chock securing the dolly’s left front wheel. The platform spun a half turn to the right, with the helicopter following it for the first 90 degrees before spiraling upward into a hover.

The pilot then set it down—prudently, one would think—on the ground, straddling the line between the ramp and the taxiway. When questioned by the tower controller, he replied, “Yeah, they didn’t chock my cart, and I was like a skateboard out here.” The controller turned him over to ground control while the line crew resecured the dolly, this time adding chocks to a third wheel.

After taking off and climbing to about 20 feet, the pilot made three more approaches to the dolly. He broke off the first two about 5 feet up.

A witness on the ramp captured footage of the third try, which ended with the helicopter hovering for about a minute before again touching down short, with the rear half of the skids hanging off. The helicopter rocked back, forward, and then back again, striking the tail skid for a second time before pitching forward, rolling right, and briefly climbing out of sight behind a hangar. FBO security cameras recorded the aircraft spinning 180 degrees left and pitching up 45 degrees.

According to the National Transportation Safety Board (NTSB) report, “the tail rotor and vertical stabilizer assembly then struck the ground and separated, and the helicopter hit the ground left side low, bounced, and rotated another 360° before landing hard on its belly. Once on the ground, the main rotor blades continued to spin, while the helicopter started spinning on its belly, as the engine continued to operate.”

Over the next five minutes, the aircraft slid some 530 feet down the ramp, spinning at a rate of about once per second until the tail boom and vertical stabilizer broke off. At that point the helicopter rolled onto its side, shearing off the main rotor blades. The engine kept running until it was smothered by fire crews.

In-cockpit images recorded by the helicopter’s Appareo Vision 1000 flight-data monitor suggest that the pilot lost consciousness at the initial impact. His passenger remained conscious for about two more minutes but could not shut off the engine or even move the collective’s throttle control from its “FLIGHT” detent. Both deaths were attributed to multiple traumatic injuries.

The Pilot

Investigators never located the pilot’s logbooks. His last four medical applications, filed during the preceding five years, all cite identical numbers: 25,000 hours of total flight experience with 200 in the previous six months. His January 2011 medical application claimed 25,400 hours of flight time.

He held a private pilot certificate with ratings for airplane single-engine and multi-engine land, single-engine sea, instrument airplane, and rotorcraft helicopter, with a type rating in the Cessna CE-525S Citation. He had earned his helicopter certification in 2001, taking his checkride in a Bell 206B-3. His application for that rating cited 14,000 hours in airplanes. Before buying the AS350, he had owned a Bell 407 and “several” Citation jets.

Three instructors who’d flown with him were interviewed during the investigation. None had ever seen his logbooks, much less made any entries in them.

The fixed-wing CFI who had given him recurrent Citation training over the past six years described him as “a high time pilot with lots of turbine jet experience” who had “owned several Citation jets and helicopters in his life and operated them for many years single pilot.”

However, the accident pilot was concerned that his reaction times had begun slowing with age. Though he had spoken of regaining currency and buying another Citation, his training had been intermittent; he had never completed the full refresher course.

The CFI believed that since his wife’s death a decade before, his client had begun “taking a more cavalier attitude toward flying; he would often let the airplane get ahead of him, [and] would not be concerned.” He characterized the pilot as “a proud and successful person, with strong ego.”

During their conversations, the accident pilot had also described his discomfort with landing the AStar, particularly “on carts,” and said that he was considering selling it. He had “agreed whole-heartedly” with the suggestion that he “just put it on the ramp” if not comfortable with the dolly landings.

The two helicopter CFIs who’d flown the AS350 with him gave similar accounts. (Both were colleagues at the company from which he had bought the ship.) The company’s chief pilot described him as “relatively competent” and “good flying from ‘A to B,’ once airborne,” but he had also insisted that the accident pilot complete the Airbus factory transition course before beginning formal training in the helicopter. He described their nine hours of dual as “familiarization/demo flights.”

His colleague flew with the accident pilot just once, for two hours on November 13. Much of that time was spent simulating dolly landings by using cracks in the pavement and taxi lines to simulate the right front corner of a cart. The accident pilot had heard that engaging the stability augmentation system would enable him to “land it like a pro,” but throughout two attempts the instructor saw him fighting the system’s inputs “with unsatisfactory results.” After that, they had turned the system off.

Both instructors noticed that previous shoulder surgery had left the pilot with limited mobility in his left arm. He was unable to climb up to inspect the rotor head during the preflight inspection and had to use his right arm to lift his left hand to the engine start switches. Both urged him not to fly without an instructor until he had completed systematic transition training and taken enough additional dual to become comfortable with the aircraft.

The chief pilot was “incredibly surprised” to learn of the accident, as he understood that the accident pilot would not fly the helicopter without supervision until he had taken the factory course. It turned out that he had registered for a B3 pilot transition course scheduled to begin November 2 but called to defer on October 31.

The Helicopter

During the flight with the second helicopter CFI, the pilot had mentioned his “5,000 hours” in the Bell 407 and complained that the AS350 “felt backwards.” There was, of course, a reason for this: while nearly identical in engine output, their main rotors turn in opposite directions.

Numerous images—from the Appareo flight recorder, security cameras at Carlsbad, and witnesses on the ramp—show the AStar yawing significantly (up to 150 degrees) just after liftoff, indicating that less than 11 hours in that aircraft hadn’t yet recalibrated the pilot’s deeply ingrained habits of pedal inputs. Further complicating his efforts to land on the dolly was the fact that the tips of the AStar’s skids are too far aft to be seen from the pilot’s seat, necessitating cultivation of other visual references. The 407’s skid tips are in clear view through the chin bubble.

The Takeaway

Reading this—or the NTSB report—it’s hard to understand why that first tailstrike didn’t convince the pilot that it was time to leave the helicopter on the ramp and resume training another day. Having at least come close to damaging a multimillion-dollar machine, why take any more risks?

For that matter, his decision to not only fly a machine he had admitted made him uncomfortable but to attempt the one maneuver he found most difficult is hard to fathom. As often seems to happen with financially gifted professionals flying high-end aircraft, the same traits that bolstered his business success—many of which also distinguish good professional pilots—may have made it hard to acknowledge even temporary limitations.

This pilot had both the background and innate ability to develop the needed proficiency … if he had taken transition training as seriously as his earlier aviation education. “If it’s got rotors, I can fly it” is an even more precarious attitude than the ­version involving wings.