Flight Operations

A Diamond in the Rough

A summary of National Transportation Safety Board (NTSB) report ERA11FA182

In early 2011, a prominent businessman, builder and community leader from Toronto lost his life in an aircraft accident in a remote area of the northeastern USA. Referred to in the NTSB report as the “pilot-rated passenger” or “PRP”, this gentleman was flying back from Halifax to Toronto in his own Diamond DA-40, accompanied by a commercial pilot whom he had hired to act as pilot-in-command. The flight planned to cross that familiar route over the State of Maine, a hilly and sparsely populated area used by many of us when flying from the Maritimes to southern Ontario or Quebec. A sophisticated machine and a strong will to make it home were no match for the dire weather conditions that awaited them enroute. Readers are invited to draw their own conclusions and hopefully learn from the account.

History of the flight

On March 7, 2011, at about 13:45 EST, a Canadian-registered Diamond DA-40 was substantially damaged when it impacted a wooded area in the vicinity of Allagash, Maine. The certified commercial pilot sustained serious injuries, and the private pilot-rated passenger was fatally injured. Instrument meteorological conditions prevailed, and an IFR flight plan was filed for the flight from Halifax International Airport (CYHZ), N.S., to Québec Jean Lesage International Airport (CYQB), Que.

According to the pilot-in-command (PIC), on the morning of the accident, he reviewed the weather with the pilot-rated passenger (PRP). He concluded that an enroute area of low pressure prevented them from flying to their final destination, Toronto/Buttonville (CYKZ). The PIC made the decision to wait until noon to re-evaluate their options. By noon, he determined that the low pressure area was moving into the Halifax area the following day. The pilots decided to depart Halifax for Saint John, New Brunswick (CYSJ) where they would wait out the weather associated with the frontal passage. They felt this would expedite the return to CYKZ.

The pilot called London International Airport (CYXU) flight service station (FSS) to file his flight plan. When asked by the FSS if he wanted a weather briefing or notice to airmen (NOTAM), the pilot declined. The flight departed IFR and reached a cruising altitude of 6 000 ft. The PIC stated that the weather in Halifax at departure was rainy with crosswinds. He recalled that they were given a clearance direct to Saint John VOR.

The PIC stated that they monitored the weather during the flight and the weather radar depiction showed mostly areas of rain. He recalled that the weather was better than forecast and that they encountered rain again as they approached Saint John VOR. The PRP questioned the PIC about continuing on to CYQB, as the meteorological aerodrome report (METAR) and terminal area forecast (TAF) looked good. The PIC reviewed the current METARs and TAFs for the area. Low ceilings and poor visibility in snow were reported. The PIC reported that the weather at CYQB appeared better, so they re-filed their flight plan with the Moncton Area Control Centre to CYQB at 6 000 ft, using St. Georges, Que., (CYSG) as their new alternate. While overflying Saint John VOR, the pilots observed that the temperature was +6°C. The flight continued within areas depicted on radar as rain. The multi-function display depicted a freezing level at 6 000 ft AGL straight ahead and a zone further ahead indicated a 4 000 ft AGL freezing level.

During the flight, the PRP advised the PIC that there was ice formation on the left wing, and the PIC observed the same thing on the right wing. The PIC described the accumulation as no higher than a nickel. The PIC asked the PRP for the outside air temperature and was told that it now indicated +1°C. They discussed the weather and agreed that the situation was not good, as they were in an area of weather that was not visible on the display and the temperature had dropped to +1°C. They discussed their options and decided to descend to a lower altitude.

The PIC requested a lower altitude from the Montreal Area Control Centre (CZUL), which authorized a lower altitude of 5 200 ft. The PIC indicated to the air traffic controller that they were experiencing icing and needed to be at a lower altitude. During the descent, the PIC recalled experiencing the most ice he had ever seen in his life; the canopy had completely frozen over. The front of the canopy and the wings were covered in ice. He described the ice as being as large as a house brick on the leading edge; the ice then extended backwards on the wing for 1 ft, with a thickness of approximately 1 to 2 in.

As they leveled the aircraft at 4 000 ft, the airspeed immediately decreased. Full power was applied, and the PIC asked the PRP to advise him if the airspeed decreased below 80 kt. The airspeed was observed at 84 kt, and buffeting was experienced in straight and level flight. Ice continued to accumulate on the airplane, and the PIC advised the PRP to start looking for somewhere to land. The airplane continued buffeting and the pilot estimated that they were approximately 1 000 ft AGL. The next thing that the PIC remembered was waking up in the airplane next to the passenger, with no recollection of how long he was unconscious. His feet were in the snow, there was no canopy on the airplane and the engine and panel were missing. He said he knew right away that the PRP was deceased.
 

Personnel information

The pilot was a licensed flight instructor with a current medical certificate who reportedly had a total of 3 000 hr of flight time, more than 1 500 hr of which were on the DA-40. He had flown approximately 20 hr in the 90 days prior to the accident. He also held a Federal Aviation Administration commercial multi-engine certificate and an instrument rating.

The PRP was the owner of the aircraft. He held a private pilot license with a visual flight rules over the top (VFR OTT) rating. He had approximately 400 hr total flight time. The flight was reportedly planned and flown as a crew, with the workload divided between the pilots. The PRP managed radio calls and monitored the outside temperature for most of the flight.

Meteorological information

The closest unofficial surface observing station was Clayton Lake, Maine, located 17 mi. east-southeast of the accident site; reported winds were from 010° at 7 kt gusting to 14 kt with a temperature and dew point of -7°C and an altimeter setting of 29.75 in. of mercury. The closest official surface observing station with ceiling and weather information was Frenchville, Maine, located 72 mi. east-northeast of the accident site. It reported winds from 020° at 18 kt gusting to 30 kt, 1 mi. visibility, moderate freezing precipitation, a broken ceiling at 900 ft AGL, a temperature of -7°C, a dew point of -9°C and an altimeter setting of 29.77 in. of mercury.

The TAF for the destination location of CYQB, as well as the closest reporting site to the accident site with a TAF, expected wind from 050° at 6 kt, visibility of 1 mi. in light snow and vertical visibility of 1 000 ft AGL. Forecast temporary conditions between 13:00 EST and 16:00 EST called for visibility of 3 mi. in light snow and an overcast ceiling at 2 500 ft.

The National Weather Service Area Forecast Discussion issued at 12:49 EST reported a band of stationary freezing rain across north central Maine due to a wedge of warm air aloft. This wedge of warm air was expected to diminish into the afternoon. Snow continued to be expected across northwest Maine with the highest snow totals located across the Maine Highlands.

Two pilot reports (PIREP) were documented before the accident time with moderate icing conditions reported across New Hampshire and Maine. Both of the aircraft that reported the moderate icing conditions had de-icing/anti-icing capability.

Wreckage and impact information

Wreckage debris and broken tree limbs were scattered about 300 ft along an approximate 200° magnetic heading from a broken tree. The airplane came to rest in approximately 6 ft of snow. The nose and the engine broke away from the fuselage and were buried in the snow. The cockpit of the airplane was exposed and the canopy broke away along the debris path. The right wing was attached to the fuselage but fragmented. The empennage broke away from the fuselage and was buried in snow along the debris path. The left wing broke away from the fuselage at the wing root and fragmented in the snow along the debris path.

Examination of the recovered airframe, engine, flight control system and associated components revealed no evidence of pre-impact mechanical malfunction. Due to the external damage, an engine run could not be performed. During the engine examination, the crankshaft was rotated by hand and valve train continuity and cylinder compression were confirmed.

Additional information

According to NAV CANADA, the flight that transitioned through the area controlled by the Boston Air Route Traffic Control Center (ZBW), located in Nashua, N.H., was an overflight westbound at 6 000 ft. There had been an airman's meteorological information (AIRMET) issued two hr earlier for light to moderate icing below 14 000 ft. The aircraft was issued vectors around mountainous terrain as per the pilot’s request, in order to stay low due to potential icing. Lost communication procedures were issued, which was standard in the area and altitude that the aircraft was transiting. The pilot switched to CZUL on his own, in accordance with the lost communication procedures issued earlier.

The pilot returned to the ZBW frequency, but the ZBW controller was unable to make contact. The CZUL controller was issuing vectors to the aircraft when radar and radio contact were lost. The ZBW controller attempted to reach the pilot through other aircraft but was unable to establish communications. A search and rescue was initiated within 30 min.

The NTSB determined the probable cause(s) of this accident to be:

The pilot's inadvertent encounter with icing conditions, which resulted in an aerodynamic stall and loss of control. Contributing was the pilots’ inadequate preflight weather planning.

Food for thought

While the report goes over the weather aspects in length, it does not explore the fine line of authority between the hired PIC and the owner pilot-rated passenger. Such an arrangement is actually not uncommon, but can be challenging and prone to additional stress. Even though the report states that they worked as a crew, the flight remained the sole responsibility of the PIC. A PIC flying with his or her boss as unofficial co-pilot, in the boss’s own airplane, may be placed in a very uncomfortable, pressure-filled position when discussing difficult weather conditions and making the go or no-go decision. Critical decision-making comes into play, particularly on the part of the PIC, but also from the owner/passenger. This report is worth a second read-through, particularly for anyone out there who faces such a situation, either as a hired PIC, or as an aircraft owner who delegates the PIC duties to someone else. —Ed.   

Flying Under the Radar—Private Helicopters

by Rob Freeman, Civil Aviation Safety Inspector, Commercial Flight Standards, Standards Branch, Civil Aviation, Transport Canada

I doubt that anyone would disagree that the helicopter is a unique invention, with its ability to hover, to operate practically anywhere and to land on an unprepared surface barely larger than the machine itself. Because of these remarkable capabilities, both private individuals and commercial operators now make up the purchasers of these machines whereas, in the not-so-distant past, helicopters were almost exclusively commercially operated. Surprisingly, the regulatory differences governing these two groups are notable, even though the flying skills and environment to operate commercially or privately are the same. Whereas the commercial regulations and standards are all-encompassing, there are minimal training and checking requirements for private operators and pilots, who are expected to take the necessary steps to ensure their own competency and currency. This situation is the same for small airplanes operated under the Canadian Aviation Regulations (CARs). 

The following extract from TSB Final Report A09Q0131, which is also summarized in Issue 1/2013 of the Aviation Safety Letter, illustrates this discussion. It relates to the investigation into the private sector helicopter accident which happened on August 5, 2009, in Mont Laurier, Que.

The investigation could not determine the pilot's experience on helicopters, but according to the log book for the Enstrom, he had flown about 300 hours on C-GVQQ since purchasing it in 1986. The pilot had received two hours of training on the EN28 in July 1986 and five hours of training on the BH06 in April 2006 to qualify for endorsement on these helicopter types. The Canadian Aviation Regulations (CARs) do not require that training records be kept for pilots in private operation. As a result, the investigation could not determine whether or not the pilot received additional flight training on the EN28 since July 1986.

Recency Requirements

To continue exercising the privileges of his licence, a pilot must comply with the recency requirements set out in CARs. The occurrence pilot was in compliance with these requirements as follows:

  1. he acted as pilot-in-command or co-pilot of an aircraft within the five years preceding the flight;

  2. he successfully completed a recurrent training program within the 24 months preceding the flight.


Wreckage of private Enstrom F-28C helicopter

Unfortunately, recent trends reveal an increase in accidents involving private pilots with causal factors tied to relatively low experience levels or lack of currency. This results in inadequate skills and poor judgment being exhibited at a critical moment—either during the flight planning decision to go, or in the air when things go wrong.

Commercial operators have some advantage here; the normal practice is to oversee the low-time pilots and to restrict the flights they are allowed to make. As a former chief pilot, I screened all flights made by our low-time pilots to protect them, our clients and our own safety record. No pilot was assigned to a job when there was any question of their currency, validity or competency. Unfortunately, there is no equivalent safety net for a private pilot who decides to take off after dusk without a night rating, or make a grand entrance and land in the parking lot at a busy restaurant or at a friend’s cottage.

Some related accident reports reveal poor decision making—flights into bad weather including forecast icing, night flights without a night rating or mandatory equipment installed, and/or failure to initiate the proper emergency procedure when problems do occur.

One example: Two private pilots in separate incidents attempted to fly back to their aerodromes of departure after mechanical problems (engine backfiring and losing power) became evident, rather than initiating immediate emergency landings. When the rotor rpm decays, ground contact, with or without pilot input, is imminent. In these cases, neither pilot was successful in their bid to continue flying, and the resulting accidents were much more severe because control of the aircraft was ultimately lost.

For those who fly infrequently or have relatively low time in type, here are a few hard facts arising from various TSB reports to (re)consider:

  • Most light helicopters are approved for day/night VFR only. That is because they do not have the natural stability to be flown on instruments without the addition of an autopilot and have no icing protection for the main or tail rotor. Any icing on the rotors can quickly become unmanageable. As well—heads up!—night flight over unlit areas, which includes most of Canada, is essentially instrument flight. The aircraft itself may be certified, but a very dark night with no discernible horizon can be as terrifying and deadly as inadvertent instrument flight in cloud or fog. Disorientation may occur as soon as the first turn away from the airport or ground lighting when the world suddenly goes black.

  • Solution: If the forecast weather or time of day does not permit you to remain within the helicopter’s certification limitations, your own abilities or your licence privileges—do not go. This requires the use of sound judgment and decision-making skills.

  • Unlike light airplanes where the engine-fuselage forward weight bias may permit a stall recovery as the nose naturally drops (altitude permitting), a helicopter main rotor that fully stalls following an engine failure will not unstall and will not respond to control inputs. In helicopters with low inertia rotors (which includes most recent models), an unrecoverable main rotor stall can develop one second or so after engine failure. You must reduce collective to the minimum within that narrow time frame and enter autorotation to preserve rotor rpm and avoid a loss of control crash. 

  • Question: Are you current with your helicopter’s autorotational procedures and confident in your own abilities if the engine quits? Important considerations include optimum speeds, limitations, glide distances and flare height. This requires regular training and practice, in order to maintain flying skills.

  • Helicopters require considerable technique to land in a small clearing, in the mountains or other areas where the available power and lift may be reduced by density altitude and/or strong down-flowing winds. The main and tail rotors of current aircraft are of a light but strong construction which does not tolerate any surface contact. Clipping a tree or rock—even slightly—with the main rotor or tail rotor may result in a complete loss of control. Precision hovering skills are critical in these scenarios to avoid collisions or rollovers.

  • Caution: Before you commit the aircraft to a landing at altitude or in a confined area, be aware that once you commit, you may not have enough power to abort or escape if things go wrong. Do you know how to calculate your aircraft’s performance to ensure a safe power margin for the intended operation? This requires judgment and skill.

You can argue that these same accidents commonly occur in the commercial sector. That is true. Unfortunately, they are more likely to occur and with more severe consequences if the pilot has relatively low experience, limited training or lapsed currency. Flying a light helicopter requires numerous skills that degrade unless structured training and emergency procedures are practiced on a regular basis. These skills are perishable and degrade more quickly in helicopters because of the number and complexity of helicopter-specific emergencies that can occur and escalate in flight.

             Canadian registered private helicopters—accidents and accident rates 2008–2012

 

2008

2009

2010

2011

2012

Canadian registered private helicopter accidentsFootnote 1

9

8

2

9

12

Canadian civil aircraft registered private helicoptersFootnote 2

741

809

851

866

880

Accident rates per 1 000 Canadian private helicopters

12.1

9.9

2.4

10.4

13.6

Accident average over 5 years equals 9.68 or approximately 10 per year.

 

             Canadian registered commercial helicopters—accidents and accident rates 2008–2012

 

2008

2009

2010

2011

2012

Canadian registered commercial helicopter accidents (703)Footnote 1

15

7

14

10

6

Canadian civil aircraft registered commercial helicoptersFootnote 2

1696

1701

1739

1790

1829

Accident rates per 1 000 Canadian commercial helicopters

8.8

4.1

8.1

5.6

3.3

Accident rate average over 5 years equals 5.82 or approximately 6 per year. 

  • For the last 5 years, private pilots in helicopters have been involved in 40% more accidents per thousand on average than comparable commercial pilots operating under CARs Subpart 703.

Footnotes

Footnote 1

Source: Transport Canada, adapted from Transportation Safety Board, preliminary data as of July 25, 2013.

Return to footnote 1 referrer

Footnote 2

Source: Transport Canada, Canadian Aviation Register.

Return to footnote 2 referrer

After conducting many check rides over the years, I’ve found that most commercial pilots with recent training and currency fly their helicopters competently and safely. From personal observation, there are two areas that seem to be consistently problematic:

  • Non-compliance with the rotorcraft flight manual limitations because of lack of knowledge; 

  • Lack of ability or familiarity with the aircraft handling procedures, particularly when demonstrating emergencies.

Both result from a lack of proper training or practice. Given the referenced accident reports, they are the same safety issues a low-time private pilot should be concerned with. The remedy is simple enough: Find a qualified person who is willing to give instruction in your helicopter or in the same model (hopefully one that is similarly equipped), with emphasis on crew resource management (what used to be called airmanship), decision-making, systems knowledge and abnormal/emergency procedures in particular. Some commercial operators, training institutions and manufacturers offer training packages tailored to their client’s needs. A quick evaluation ride and a few targeted questions will establish a baseline and identify what training needs to be accomplished.

Training is not cheap, but what value do you place on your own life or that of your passengers? If you are not undergoing recurrent training at least once a year, you may not have the skills, knowledge or judgment to respond correctly when things go wrong. The bottom line is that helicopters are more complex and demanding to fly than light airplanes and those specialized skills have a best before date. Going extended periods without flying a helicopter and without recurrent training is the thread that connects many of these private sector accidents.

In addition to the 2009 Mont Laurier occurrence linked earlier (A09Q0131), the following three links to other private helicopter accidents also illustrate these issues and may be of interest: TSB Final Report A09Q0210, TSB Final Report A05P0154 and TSB Final Report A09O0207.

Carburetor Icing Likely Cause of Downed Piston Helicopter

The following article is based on TSB Final Report A11O0222—Collision with Terrain and is presented to highlight the hazard of carburetor icing in piston-engine helicopters

Summary

On November 28, 2011, a Robinson R22 helicopter departed the Region of Waterloo International Airport (CYKF), Ont., for a local training flight with a student and instructor on board. The preflight inspection, start-up and engine run-up were completed near the company’s hangar and the crew air taxied the R22 to a grassy departure area south of the approach path to Runway 08. There was a short delay due to tower frequency congestion. During this 5-min time period, the crew decided to practice touchdowns and lift-offs from the hover. At 11:30 EST, the air traffic controller cleared the crew to lift off and make a turn around the control tower for a southbound departure. Approximately 1 min after takeoff, the helicopter crashed in a drainage swamp on airport property, fatally injuring the instructor and seriously injuring the student. The helicopter was destroyed by impact forces; there was no post-impact fire.


 

Accident sequence

The aircraft lifted off from the grassy area with the student pilot in control and proceeded as instructed by the air traffic controller. After reaching approximately 200 ft AGL, at a typical departure speed, southbound over an area of multiple hangars and overhead wires, the instructor instructed the student to apply carburetor heat. It is not clear whether this instruction was actioned; however, shortly thereafter, the engine shuddered, the engine rpm decreased, and the instructor assumed control. The helicopter yawed first to the left then back to the right and began to descend. At 11:31 EST, the R22 impacted the ground in a level pitch attitude with little forward velocity.

The crash site was a 4-ft deep drainage swamp on the airport’s southern perimeter, approximately 60 ft short of an open field. The helicopter was destroyed. The instructor was fatally injured by the vertical impact force, and the student was seriously injured.


Flight path

Other information

The weather was appropriate for VFR flight. The wind was light and variable, the visibility was greater than 9 SM, the ceiling was overcast at 1 300 ft AGL, the temperature was 4°C and the dew point was 1°C. It had rained most of the previous day and at the time of the occurrence, the ground, including the grassy area, was very wet.

The instructor was licensed and qualified in accordance with existing regulations. In addition to the required training, a Robinson Helicopter Company Pilot Safety Course was completed by the instructor in December 2008, which focused on emergency procedures including autorotation. At the time of the occurrence, the instructor had approximately 1 040 total flight hr, mostly on Robinson helicopters. The instructor was off duty the preceding two days and the occurrence flight was the second flight of the day. The student pilot had approximately 18 total flight hr, the most recent flight being one week earlier.

The aircraft was equipped and maintained in accordance with existing regulations and was being operated within published weight and balance limitations. It was equipped with a Lycoming O320-B2C engine: a 4-cylinder, carbureted, normally aspirated engine producing 160 horsepower. The engine controls include a twist grip throttle, fuel mixture control, carburetor heat control and an rpm governor. The following gauges are installed to monitor engine performance: engine and rotor dual tachometer, manifold pressure gauge, ammeter, oil pressure and temperature, and a carburetor air temperature gauge.

The fuel mixture and carburetor heat controls are located on the centre pedestal in close proximity to each other. To aid in identification, the control knobs are shaped differently. Furthermore, the fuel mixture control knob is red while the carburetor heat control knob is black (Photo 1). To prevent inadvertent deployment in flight, the manufacturer’s checklist directs the pilot to place a removable cylindrical plastic guard over the mixture control knob before starting the engine (Photo 2). This guard is not to be removed until engine shutdown when the mixture control knob is pulled to the idle cut-off position (Photo 3). This plastic guard is not permanently attached to the control panel.


Photo 1: Mixture control top right and carburetor heat control bottom right


Photo 2: Mixture control with guard installed


Photo 3: Mixture control in idle cut-off position

Wreckage examination

The crash site was a drainage swamp on the airport perimeter which had thin wires strung across it in a checkerboard fashion to prevent birds from occupying it. The helicopter’s position amongst the wires indicated a near vertical descent. Most of the damage and deformation to the helicopter was on the bottom surface, which is consistent with a near vertical impact with little forward velocity. One of the main rotor blades was bent in a fashion consistent with coning, which may have resulted from low rotor rpm in flight or from impact with the water. There was no evidence of rotor mast bumping or main rotor blade contact with the tail boom.

There were no pre-impact mechanical failures or system malfunctions that would have contributed to this accident. A teardown of the engine and accessory gearbox revealed that although they were serviceable, they were not turning at impact. The plastic mixture guard was not found at the crash site. The fuel mixture control was found in the full rich position. The carburetor heat control knob was found in the cold position. Examination of the cable-operated guillotine valve in the carburetor air box confirmed that the carburetor heat was selected to cold prior to impact.

Carburetor icing

Carburetor icing is a phenomenon where the temperature of air entering the carburetor is reduced by the effect of fuel vaporization and by the decrease in air pressure caused by the Venturi effect. If water vapour in the air condenses when the carburetor temperature is at or below freezing, ice may form on internal surfaces of the carburetor, including the throttle valve. As ice forms, this increases the Venturi cooling effect due to the narrowing of the carburetor throat, and this narrowing reduces power output. Unchecked, the ice can quickly lead to a complete engine failure. To overcome carburetor icing, aircraft manufacturers provide a system to heat the incoming air and prevent ice accumulation.

Unlike piston-powered airplanes, which normally take off at full throttle, helicopters take off using only as much power as required. This partial throttle position makes them more vulnerable to carburetor ice, especially when the engine and induction system are still cold. The Robinson R22 is equipped with a throttle governor which can easily mask carburetor icing by automatically increasing the throttle to maintain engine rpm, which will also result in constant manifold pressure. To alert pilots to the possibility of carburetor ice, the helicopter is also equipped with a carburetor air temperature (CAT) gauge which displays a yellow arc outlining the range of temperatures to be avoided during possible icing conditions. Robinson R22 pilots are instructed to apply carburetor heat as required to keep the CAT out of the yellow arc during power settings above 18 in. manifold pressure and to apply full carburetor heat at settings below 18 in.

If significant ice is allowed to develop within the carburetor and full heat is applied to melt it, the resultant water flow through the engine causes the engine to run rough temporarily and to lose further power.

To help determine whether flight conditions are more or less susceptible to carburetor ice, charts based on a knowledge of dry (ambient) and wet (dew point) air temperatures have been produced. The temperature and dew point at the time of the occurrence when referenced against these charts describe the conditions as the most severe or “serious icing – any power”. In addition, the likelihood of accumulating ice can be exacerbated by operations in cloud, fog, rain, areas of high humidity, or in this case, ground operations over wet surfaces, especially wet grass.


Carburetor icing probability chart

Low rpm rotor stall

The manufacturer notes that rotor stall due to low rpm causes a very high percentage of light helicopter accidents (refer to linked safety notices SN-10 and SN-24 in next para). This risk is greatest in small helicopters such as the R22 which have low main rotor blade inertia. When engine power is lost, the collective must be lowered immediately, which induces a rate of descent. If this rate of descent is reduced by raising the collective, the rotor rpm will be reduced. If the rpm is reduced too much, the rotor will stall and no longer provide the lift required to support the helicopter.

Robinson Helicopter Company safety notices

Following a series of accidents and incidents, the Robinson Helicopter Company issued safety notices (SN) to its operators to reduce the likelihood of similar accidents. These are published on their Web site and at the back of their pilot’s operating handbook (POH). Of particular relevance are the following SNs:

Analysis

The helicopter’s engine was not running at impact although there were no mechanical anomalies that would have prevented its operation.

The weather conditions at CYKF were highly conducive to carburetor icing. In addition to the temperature/dew point spread, the operation conducted over wet grass would have intensified the rate of ice accumulation.

The investigation could not determine whether the carburetor heat control was adjusted as required to keep the CAT out of the yellow arc during the period the helicopter was hovering over wet grass or during takeoff. However, when the helicopter struck the ground, the carburetor heat was selected to cold. This cold selection may have been the result of not applying carburetor heat; or if it was applied after ice had formed in the carburetor and the immediate result was a rough running engine, the carburetor heat may have been de-selected. In either case, the engine likely stopped due to ice blocking the airflow through the carburetor.

An instructor flying with a relatively new student would likely be carefully monitoring the student’s actions, particularly during the critical takeoff phase. The possibility that the mixture control was inadvertently selected to idle cut-off was considered to be unlikely as the student would have had to remove the mixture guard, pull the mixture control to idle cut-off and return it to full rich without the instructor’s intervention. In addition, the fact that the carburetor heat, which would have been required given the conditions, was found in the cold position would further suggest that this scenario is unlikely.

At the time the engine failed, the position of the helicopter would have made a successful autorotation very difficult; it was at low altitude over a group of hangars with multiple overhead wires strung between numerous poles. The closest spot which was free of obstacles was the field 60 ft beyond the crash location.

The quick yawing following the engine failure most likely resulted from torque changes due to power loss. This yawing would have decreased forward velocity and increased the angle of descent. In an attempt to decrease the angle of descent and reach the field, the pilot likely raised the collective causing the rotor rpm to decrease to a point which could no longer sustain flight. The helicopter subsequently fell almost vertically into the swamp area short of the field.

Findings as to causes and contributing factors

  1. Environmental conditions were conducive to serious carburetor icing. It could not be determined if carburetor heat was applied.

  2. The helicopter’s engine failed during departure, most likely due to ice accumulation in the carburetor.

  3. The departure path took the helicopter over an area of buildings and obstacles, which would have made a successful autorotation difficult.

  4. The pilot likely raised the collective in an attempt to reach a suitable field, causing the rotor rpm to decay to a point which could no longer sustain flight. The helicopter subsequently fell, almost vertically, into the swamp.

Dressed for survival

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