- Issue 4/2010
- Copyright and Credits
- Flight Operations
- Maintenance and Certification
- Recently Released TSB Reports
- Accident Synopses
- Regulations and You
- Debrief: Déja vu: The Importance of the Underwater-Egress Pre-Flight Briefing for Passengers
- Self-Paced Study Program
- Full HTML Version
- PDF Version
- Major Accident Report: Bell 206 Down in
- What Went Wrong: In-Flight Blackout
The following is a condensed version of Transportation Safety Board of Canada (TSB) Final Report A08P0125, on the fatal crash of a Bell 206B Jet Ranger helicopter in Cranbrook, British Columbia. Readers are encouraged to read the full report on-line at www.tsb.gc.ca.
On May 13, 2008, a Bell 206B Jet Ranger with the pilot and two passengers on board took off on a mission to visually examine electrical power transmission lines that ran through the city of Cranbrook, B.C. To accomplish this task effectively, it was necessary for the inspection to be carried out at about 20 to 30 ft above the line or pole heights, at a ground speed of 25 kt. At about 13:06 Mountain Daylight Time (MDT), as the helicopter was flying southbound at about 120 ft above the ground, a sudden loss of engine power occurred causing rapid loss of rotor RPM. The helicopter descended quickly and landed heavily on a paved street below the flight path. The helicopter struck a pedestrian on the sidewalk adjacent to the impact point, as well as a motor vehicle. The helicopter broke into several pieces and burst into flames. The three occupants of the helicopter and the pedestrian were fatally injured at impact.
The aircraft was flying south-southwest over 14th Avenue (midway between 7th and 10th Streets), at about 120 ft above ground level (AGL) and 25 kt, when the engine lost power. The final few seconds of flight were uncontrollable and in free-fall from about 85 ft AGL. The weather conditions did not contribute to the accident circumstances, and the experienced pilot was certified and qualified for the flight. The helicopter was certified, equipped, and maintained in accordance with existing regulations and procedures.
The accident site was generally an open area but there were several obstructions that the pilot may have tried to avoid during descent, namely the residential power lines, tall trees, several houses, and vehicular traffic. Given those obstructions, it is unlikely that the pilot saw either the pedestrian or the car before impact. The airframe wreckage was examined to the extent possible by the TSB, and for the few airframe components that did survive the fire, no indication was found of any pre-accident anomaly or malfunction. The TSB also determined that the weight, centre of gravity (CG), as well as hover out of ground effect (HOGE) performance were all within prescribed limits.
The engine, fuel control unit (FCU) and power turbine governor (PTG) were disassembled and examined in detail. They had been exposed to extreme temperatures during the post-crash fire and had suffered significant damage. The TSB tests showed no mechanical anomaly that could have affected their function; however, a latent malfunction of either the FCU or the PTG could not be ruled out. (For more details, including references to a 2005 investigation on a similar PTG, readers should refer to the complete TSB Final Report on the TSB’s Web site. —Ed.)
A critical aspect of autorotation is the entry manoeuvre immediately following the loss of engine power because the pilot must react quickly to conserve rotor RPM. Of the other factors affecting autorotative flight, the altitude at the time of the loss of engine power immediately establishes several important elements of successful descent and landing. The greater the height above the landing surface, the greater choice of suitable landing areas, the more time to establish and maintain control of the helicopter, and the longer the glide distance. Low-altitude flight reduces all these margins to the point where successful autorotative flight and landing may be impossible.
Telemetry data from the helicopter allowed investigators
to recreate the flight path, depicted above.
The no-engine landing after an autorotative descent is a challenging manoeuvre for any helicopter pilot since it involves skills not frequently practiced within an unforgiving flight regime. For this accident, several obstacles greatly restricted the pilot’s manoeuvring and choice of landing sites. Further, he was faced with the dilemma of extending the glide to avoid the houses at the expense of controlled flight. In these circumstances, the pilot had insufficient altitude to maintain functional rotor RPM following the engine power loss, and the final few seconds of flight were uncontrollable and in free-fall from about 85 ft above the road.
Tail rotor unit shown at the accident scene. The main and tail
rotor blades were relatively undamaged.
Height velocity diagram
The height velocity diagram (HVD) (see below) shows, in graph format, those combinations of airspeed and height above the ground where either a fully developed autorotative glide can be entered or a safe landing carried out after the single-engine helicopter suffers an engine power loss. The HVD is not a limitation in the flight manual, but rather a guide to show the flight profiles where pilots are exposed to the greatest risk resulting from engine power loss, and so identifies height and speed combinations to avoid or pass through quickly. The HVD for the Bell 206B shows that a pilot should not expect to establish full autorotation from heights between 40 and 200 ft AGL, unless the airspeed is above 45 mph. In this case, the helicopter was at about 120 ft AGL and travelling at about 30 mph; with such height and speed, the helicopter could not have achieved full autorotation before it struck the ground.
Regulatory requirements for flight over built-up areas
The following sections of the Canadian Aviation Regulations (CARs) and Commercial Air Service Standards (CASS) prescribe the altitudes at which aircraft may be flown: CAR 602.14—Minimum Altitudes and Distance; CAR 602.15—Permissible Low Altitude Flight; CAR 702.22—Built-Up Area and Aerial Work Zone; and CASS 722.22—Built up Area and Aerial Work Zone. The accident flight was involved in aerial inspection as a commercial operation, in which case it would be bound by the requirements of Part VII of the CARs.
The company was operating under the auspices of its subpart 702 certificate—Aerial Work. Subsection 702.22(2) allows a person to operate over a built-up area at altitudes and distances less than the general prohibition if the person: is so authorized by the Minister, or is authorized to do so in an air operator certificate; and complies with the CASS. To obtain such authority, subsection 722.22(1) of the CASS requires an aerial work zone plan to be submitted to the Transport Canada Aviation Regional Office at least five working days in advance of the operation, and prescribes the information that must be submitted. Furthermore, subsection 722.22(3) lists additional requirements related to this application. In this case, the operator had not applied for, or received, authorization from the Minister of Transport, nor had it submitted an aerial work zone plan.
Low-altitude aerial inspection flights over built-up areas have been undertaken in Canada for at least the past 30 years, and regulatory requirements for such flights have existed in one form or another throughout. The TSB determined that much misunderstanding exists regarding the interpretation and application of altitude requirements in the CARs and associated CASS. In all likelihood, low-altitude aerial inspection flights are being carried out over built-up areas in Canada without full compliance with regulatory requirements.
The cause of the loss of engine power was not determined. No evidence was found to suggest that any of the engine modules had suffered any pre-impact mechanical event that would have contributed to a loss of engine power. The accident FCU and PTG were damaged, and while it is possible that either one malfunctioned, the TSB could not make a definitive conclusion on them.
Several operational conditions existed to present the pilot with a greater-than-usual challenge for an emergency landing following the loss of engine power, namely:
- obstructions on the final flight path;
- low airspeed;
- low height above the terrain;
- low rotor RPM; and
- short time frame.
The above factors individually represent significant difficulty for a pilot to achieve a successful outcome, but when combined, they pose operational challenges that a pilot may not overcome.
The HVD shows that low altitude and low airspeed combinations present a significant challenge to pilots in landing successfully from an event that requires an immediate landing. On the diagram, such higher-risk zones are labelled “avoid” areas and represent the worst circumstances for recovery. The accident helicopter was frequently exposed to the higher-risk avoid zones of the HVD during its passage over the built-up areas of Cranbrook.
Height velocity diagram
The CARs prescribe conditions for low-altitude flight in helicopters over built-up areas that, in general, ensure the manner of operation does not create a hazard, and that the altitude (height) of a flight is such that an immediate landing can be made without creating a hazard. Information contained in the flight manuals (such as the HVD) assist operators and pilots in choosing the most appropriate flight profiles for their missions and take into account helicopter performance. Accordingly, the final responsibility for safe operational practices remains with individual helicopter operators and pilots. The severity of this accident was influenced by the low altitude and airspeed, and the landing site environment.
The requirements governing flights over built-up areas are found in several areas of aviation regulation; they are complex and subject to wide interpretation, such as when an aircraft is or is not over a built-up area and which requirements would apply where and under what circumstances. The helicopter performed manoeuvres over homes in the vicinity of the power lines. Therefore, the accident flight took place over a built-up area. In the absence of clear direction and guidance, companies may select the requirements that impose the least stringent conditions. Therefore, low-level aerial inspection flights over built-up areas will continue, thereby creating a hazard to persons and property on the surface.
Findings as to causes and contributing factors
The engine lost power at an altitude and airspeed combination that did not permit fully developed autorotative flight, resulting in rapid loss of rotor RPM, an extremely high rate of descent, and a severe collision with the terrain.
The helicopter was being operated at a height and airspeed combination that the helicopter manufacturer had determined would, in the event of an engine power loss, preclude a successful descent and landing.
During the final seconds of the flight path, the pilot was hindered by several obstacles that afforded him only one clear landing site, which was beyond the gliding range of the helicopter. The pilot’s efforts to avoid the house and reach that site exacerbated the already high rate of descent.
- The helicopter was not in a controlled descent and, coupled with the decaying rotor RPM, the pilot’s ability to control the helicopter was decreasing so rapidly that the last 85 ft of height were in free-fall.
Flights conducted at altitudes that do not permit safe descent, manoeuvring and landing following an event that requires a single-engine helicopter to land immediately create risk to persons and property, particularly in built-up areas.
- The CARs requirements for low-level aerial inspection flights over built-up areas are complex and subject to wide interpretation. In the absence of clear direction and guidance, companies may select the requirements that impose the least stringent conditions. Therefore, low-level aerial inspection flights over built-up areas will continue, thereby creating a hazard to persons and property on the surface.
Safety action taken
Transport Canada (TC) had considered the publication in the ASL of a “logic chart” to guide pilots and operators in correct decision making regarding the minimum altitudes and distances over built-up areas prescribed by the CARs; however, upon further review, it was determined to be inadvisable for the intended purpose, and that guidance in this area would be better included in the Transport Canada Aeronautical Information Manual (TC AIM). Therefore, TC is now planning to publish updated guidance on flight over built-up areas in a future update of the TC AIM.
The operator revised its operational practices regarding low-altitude flight and introduced a higher level of internal oversight. Additionally, it embarked upon a dedicated safety management system (SMS).
Finally, BC Hydro took immediate and long-term actions to address its policies and associated procedures concerning the use of helicopters, and the development and implementation of a more extensive helicopter management system.
by R. Wicks. The following article was originally published in the March-April 2007 issue of Flight Safety Australia and is reprinted with permission.
An electrical fault knocks out several key systems including engine computers, NAV and COM equipment, flight instruments, flap, and landing gear.
I was transporting several passengers, and 10 NM from Adelaide [South Australia] in instrument meteorological conditions (IMC), when I heard a clunk from somewhere on the left side of the Cessna Conquest C441’s cabin.
Light misty rain streaked up the windscreen and I was at 3 000 ft and had just been cleared for a Runway 05 VOR [VHF omnidirectional range] approach via the 10 NM arc.
The clunk was accompanied by the appearance of red flags on the primary attitude indicator (AI), horizontal situation indicator (HSI), and altimeter. The left-hand engine instruments were out too (torque, EGT [exhaust gas temperature], fuel flow, temperatures and pressures) and the left-hand fuel computer had tripped as well.
Without the fuel computer, which controls engine RPM and torque (among other things), the left-hand engine RPM surged from 96 to 100 percent. To make matters worse, the autopilot bell sounded to indicate that it had disconnected.
The priority was to fly the aircraft and see if I could work out what was happening. The artificial horizon (AH) on the co-pilot’s side was operational, as was the co-pilot’s directional gyro (DG).
I levelled the wings and increased the right-hand engine RPM to 100 percent to get rid of the distracting drone generated by the out-of-sync propellers.
With the aircraft stable, I had to make a decision about what I was going to do next. I called Adelaide Approach on COM1, but there was no response. I set the transponder to 7600, and checked VOR1—another red flag. How was I supposed to do an 05 VOR approach? Or even an ILS [instrument landing system]?
I made another call on the radio but there was no reply. My scan came to the GPS—yes, it was working! Thankfully, it was wired to the hot bus.
I was now 6 NM from Adelaide with a groundspeed of 180 kt—just two minutes from the airport. I was high, but that wouldn’t be a problem in the Conquest.
With my local knowledge of the airport and the fact that I was arriving from the west, over the sea, I decided to descend until I could see the coast and make a visual approach.
Visibility was now about 2 km, and I could see the ocean below. I entered “direct to” in the Trimble and quickly got a bearing to the airport (I was surprised that I had turned right and needed a left turn of 20° to compensate.)
A Boeing 737 had started a VOR approach a few minutes before and I hoped the approach controller knew I was experiencing problems and was keeping us separated.
I selected approach flap but the electrically driven flap motor was silent. What about the landing gear? I moved the lever to the down position—again, no response. On top of everything else, I was going to have to carry out an emergency gear extension and make a flapless approach. A small bead of sweat formed on my lip—a sure sign of stress. I checked that the gear selector was down, pulled the circuit breaker and pulled the “T” handle—nothing!
I was barely a kilometre from the coast but still could not see it. What now? I was approaching the very limit of my reasoning ability with the intense pressure of the situation.
“Is everything alright?” asked the passenger next to me. I figured he was wondering why I kept looking at the AH on his side of the cabin. I answered, “Yes,” then really yanked on the handle.
Yes—I had three greens! I could also just make out the faint outline of the coast. I did a quick landing check, extended the landing lights and turned off the right-hand fuel computer (both need to be off for a “manual” landing).
I flashed my landing lights and got a green flash in return from the tower, indicating I was cleared to land.
We touched down safely and I remembered not to use reverse thrust with the fuel computers not functioning. After landing, I received a green light to taxi and park the aircraft, though my troubles weren’t quite over. The “stop” button failed to shut down the left engine and in the end I had to use the condition lever, which cuts off the fuel, to bring it to a halt.
Several passengers thanked me for a great flight as they disembarked. If only they knew!
What happened? The rear bearing in the left-hand starter generator failed, causing the armature to short on the casing. Consequently, the 225-amp current-limiter blew and all items on the left-hand main bus failed.
Following this incident, the company obtained a diagram showing the aircraft’s electrical distribution. This diagram is not included in the pilot’s operating handbook.
Although COM2 was functioning, this aircraft had only one audio panel and its “Emerg” position supplies power to audio panel one for transmission on COM1.
NAV2 had been working, though I didn’t realize it until I was visual. I spoke to the approach controller later and he told me there was no issue with the B737. He instructed the jet to overshoot when he lost my paint and couldn’t reach me on the radio. Well done!
Analysis (by Mike Smith, aviation consultant)
Good situational awareness, prioritization of tasks and sound decision-making skills helped this pilot out of a very unpleasant situation. It is often said that single-pilot IFR flying is one of the most challenging tasks a pilot can undertake and it is because of precisely this type of occurrence that it is so challenging.
An instrument approach in cloud and rain, and in a complex aircraft such as the Conquest, when everything is going well is hard enough; add in the failure of some essential equipment, and the workload can become so great that sound decision making often goes out the window.
This pilot had good situational awareness and he used that to his advantage to solve the problem caused by the loss of his primary VOR. Becoming visual over the sea and making a visual approach over familiar terrain would have eased his workload considerably. He also had a fair idea about the position of the 737 and presumed correctly that ATC would take care of the situation.
The electrical system on the Conquest is designed to cope with numerous failures and still retain the ability to operate flight-critical systems. In this case, not only did the left engine starter-generator fail but it also caused a short that blew the associated current limiter.
Were it just a straight-out generator failure, without a short, the problem would be simple; in all likelihood, the right engine starter-generator would have continued to power most aircraft systems through the tie-bus. The pilot would have been alerted to the off-line left-hand generator and would simply have had to manage electrical load to below the capacity of the remaining generator, in the case of the Conquest, about 200 amps.
But the short apparently caused the current limiter to isolate the left-hand main bus from the available electrical supply. It may be possible that power could have been restored but that would have required a detailed knowledge of the electrical distribution system and that information was not available to our pilot. It is pleasing to read that the company has now made available the necessary information for its pilots.
In any case, with the high workload occasioned by the instrument approach and the loss of several aircraft systems, including engine computers, NAV and COM equipment, flight instruments, flap, and landing gear, this pilot made a series of wise decisions that eased his workload and enabled him to concentrate on a safe visual approach and landing.
How well do you know the systems on the aircraft you fly? What’s it like to do an emergency gear extension for real? What’s the effect on landing distance of having no flap or engine reverse thrust available?
The airlines have comprehensive training and checking regimes, and the advantage of flight simulators to ensure their crews are current and equipped to deal with the sort of emergency this pilot experienced. Most of us flying single-pilot IFR, like the pilot in this story, do not have this facility, so constant review of aircraft systems and drills is necessary to ensure our mental workload is not too taxing when something does go wrong.
by Steven Schmidt. This article was originally published in the November-December 2008 issue of Flight Safety Australia, and is reprinted with permission.
It was the mid-80’s and I’d just earned a level 2 (junior) instructors’ ticket at a gliding field in central Victoria [Australia]. The previous week had been wet, and it was touch and go whether we operated at all.
We decided to operate with one aircraft—a two-seater tandem trainer called a Blanik. It had medium performance and behaved well on the winch. By operating only one aircraft with an instructor required on board, the CFI [chief flight instructor] was confident we could keep operations to the centre of the landing strip and avoid getting bogged.
Debbie was my first customer for the day. She had been solo several years earlier, but her attendance to the field had been dropping off and her currency was decaying. Debbie could be described as a high maintenance pilot given to emotional outbursts and stubbornness.
The single-glider operation resulted in a slow turnaround, and Debbie was obviously irritated by this. When I asked her to complete a pre-takeoff inspection of the aircraft I got an immediate and aggressive response.
“Why? I’ve just seen the glider take off and land without mishap.” I responded with a pat answer and thought to myself that it was not a good beginning for an experienced pilot. I had a growing sense of foreboding.
We both jumped into the Blanik and strapped in. The retrieve car was still running out the cables from the winch, so we had plenty of time for a briefing.
“The day is stable so there will be no lift. It’s a good opportunity for circuit practice and spot landing. I would like you to do the launch, circuit and landing as you have done many times before,” I briefed Debbie.
Propelled by the cable, she introduced back elevator smoothly, and we were climbing. I was in the back seat, where it is difficult to see at the best of times. As we started the launch, I caught a movement on the taxiway to our side. Once we had rotated into full climb, I could see a Piper Cherokee approaching the strip along the taxiway.
The launch was nearly text-book perfect and as we neared the top of the launch Debbie eased the elevator fractionally forward to release the tension on the cable before releasing.
She established glide speed and completed her post-launch checks. Without prompting, she spent a few moments re-familiarising herself with the aircraft and entered the circuit. She ran through her pre-landing checks early and quickly. Once settled on the downwind leg I asked, “Anything unusual about this circuit you may consider planning for?”
“No,” was her response.
“Well, if it were me I’d be planning for that Piper backtracking on the runway where we wish to land.”
“Smartass!” was the reply.
To those on the ground, we
missed each other by feet.
We agreed to stay high in circuit to maximize our landing options.
As we turned onto the base leg the Piper stopped, facing us. “As large as the Blanik is, it still may be difficult to see. We have no radio, so ‘S’ turns will profile the aircraft and should make it easier to see us on base leg,” I advised. At the same time the Piper did a 180-degree turn into wind and faced the end of the strip.
The Piper had stopped and did not move for the duration of our final leg. Debbie, who was now focused on the task declared, “He’s stopped and waiting for us.” I agreed, without further consideration.
Debbie established an aiming point for the landing deep within the strip. She was landing long to avoid the Piper and deployed the airbrakes to increase the descent rate accordingly. My focus now, like Debbie’s, was on her landing.
Airmanship should always
be practised. It’s sad, but like
common sense, often such states
of mind seem very uncommon.
Unbeknown to both of us was the fact that the Piper pilot, having completed his run-ups into wind, had pushed the throttle forward. To those on the ground, we missed each other by feet.
Debbie’s landing was excellent, but my enthusiasm was immediately crushed with the news of the near collision. Later that evening the visibly shaking pilot of the Piper approached me. He seemed sorry but asked, “Why didn’t you stay up longer? I saw you launch and expected that I had plenty of time to take off.”
I replied, “It was a winter’s day, stable and no lift except from the winch, average circuit times are 6–8 minutes depending upon the launch.”
To which he replied, “You are
too small to see.” I took this
reply with a grain of salt. The
Blanik is almost 28 ft long
with a wing span of 53 ft.
He then asked, “Why didn’t you broadcast your intentions?”
With a little exasperation in my voice, I responded, “Our gliders do not have electrical systems and the Blaniks, which have been here for five years, have never had radios. We ‘S’ turned on base so you could see us.” To which he replied, “You are too small to see.” I took this reply with a grain of salt. The Blanik is almost 28 ft long with a wing span of 53 ft. I thought to myself that he didn’t really look. I then asked, “Why, having turned into wind, did you not take off immediately?” He replied sheepishly that he had not done his pre-takeoff checks.
Twenty-five years later, I have different views. The Piper pilot clearly demonstrated poor airmanship irrespective of the breach of CARs [Australian Civil Aviation Regulations]. He did not think through his actions and put himself in a position where he could not observe incoming traffic, or give way to that traffic, as required by law and good sense. For our part, our lack of understanding of the need for a run-up into wind and pre-takeoff checks concluded in a naive assumption that the Piper pilot had seen us on final leg and was waiting for us to land.
I recognize that I had been distracted by Debbie’s behaviour and a desire to pass on my training messages effectively, unfortunately at the cost of safety. Although visibility from the back seat, especially underneath the glider, was limited, I should have been more vigilant in checking her lookout, particularly in regards to the Piper. We still had height, whilst crossing the airfield threshold, to make some avoidance manoeuvres.
Airmanship should always be practised. It’s sad, but like common sense, often such states of mind seem very uncommon. Having said this, we must still always strive for that elusive goal, for all our sakes.
TC AIM Snapshot—Flight Operations in Rain
An error in vision can occur when flying in rain. The presence of rain on the windscreen, in addition to causing poor visibility, introduces a refraction error. This error is because of two things: firstly, the reduced transparency of the rain-covered windscreen causes the eye to see a horizon below the true one (because of the eye response to the relative brightness of the upper bright part and the lower dark part); and secondly, the shape and pattern of the ripples formed on the windscreen, particularly on sloping ones, which cause objects to appear lower. The error may be present as a result of one or other of the two causes, or of both, in which case it is cumulative and is of the order of about 5° in angle. Therefore, a hilltop or peak ½ NM ahead of an aircraft could appear to be approximately 260 ft lower, (230 ft lower at ½ SM) than it actually is.
Pilots should remember this additional hazard when flying in conditions of low visibility in rain and should maintain sufficient altitude and take other precautions, as necessary, to allow for the presence of this error. Also, pilots should ensure proper terrain clearance during enroute flight and on final approach to landing. (Ref: Transport Canada Aeronautical Information Manual, Section AIR 2.5)
2010-2011 Ground Icing Operations Update
In July 2010, the Winter 2010–2011 Holdover Time (HOT) Guidelines were published by Transport Canada. As per previous years, TP 14052, Guidelines for Aircraft Ground Icing Operations, should be used in conjunction with the HOT Guidelines. Both documents are available for download at the following Transport Canada Web site: www.tc.gc.ca/eng/civilaviation/standards/commerce-holdovertime-menu-1877.htm.
If you have any questions or comments regarding the above, please contact Doug Ingold at firstname.lastname@example.org.
Call for Nominations for the 2011 Transport Canada Aviation Safety Award
Do you know someone who deserves to be recognized?
The Transport Canada Aviation Safety Award was established in 1988 to recognize persons, groups, companies, organizations, agencies or departments that have contributed, in an exceptional way, to aviation safety in Canada.
The Award—a certificate and letter signed by the Minister of Transport—is presented to the recipient the week of National Aviation Day (February 23).
Any individual, group, company, organization, agency or department may be nominated for this Award. The nominee must be a Canadian-owned organization or a resident of Canada.
Nominations must demonstrate that the contribution to aviation safety meets at least one of the following:
A demonstrated commitment and an exceptional dedication to Canadian aviation safety over an extended period of time (three years or longer);
The successful completion of a program or research project that has had a significant impact on Canadian public aviation safety;
- An outstanding act, effort, contribution or service to aviation safety.
The closing date for nominations for the 2011 award is December 7, 2010. For complete details, including the on-line nomination form, visit:
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