Cranbrook Heli Crash (2008) [Speculation & Commentary]

[Ogee]

You are correct, well-spotted.

[Ogee]

This is an interesting bit in a little dispute about terms by a couple of the lads over in the helicopter forum. It has to do with Vortex Ring State or settling with power. I don't mean to continue the argy bargy here, but this bit from the TSB could possibly apply to what happened in Cranbrook.

One thing is different. There is the report of visible rotor blades and the rotor blades remained pretty well as they normally are on the wreckage prior the things melting down in the fire.

Anyways, for what its worth...

Aviation Investigation Report
Collision With Terrain
Helimax Ltd.Hughes 369D
(500D) Helicopter C-GYTY
Baffin Island, Nunavut, 69º10' N 074º21' W
09 August 2001
Report Number A01Q0139

Summary
A Hughes 369D (500D) helicopter, C-GYTY, serial number 270078D, was being used to transport geological survey personnel and geological samples. The helicopter had picked up two passengers and one sample cache and was in a circling descent for landing at another cache. During the final approach, the helicopter struck the ground heavily, bounced, and tumbled. The pilot was fatally injured on impact. The passengers survived the impact, but later succumbed to their injuries. The helicopter was destroyed by impact forces and a post-impact fire. The sky was clear and winds were light and variable. The accident occurred at about 1700 eastern daylight time.

Ce rapport est également disponible en français.


Other Factual Information
The float-equipped Hughes 369D (500D) helicopter was proceeding along a traverse line to retrieve geological samples that had been placed at intervals along the line. While en route to the second cache location, the pilot made a radio transmission to personnel further along the traverse line. The helicopter was observed overflying the second cache site and, from an estimated altitude of 200 feet above ground, started a tight clockwise descending turn to land at the cache location. The helicopter flew a steep, descending, right turn through 270 degrees and continued the descent toward the cache. Ground personnel heard a brief, unintelligible radio transmission, believed to be from the pilot. Shortly thereafter, a large plume of smoke was seen to rise from the accident site.

The terrain was hilly and rock covered. The helicopter, in forward flight, at a high rate of descent, and in a 25-degree nose-down attitude, struck the ground just below the crest of a hill. On impact, the right float and skid tube dug into the surface, and the left float broke free from the helicopter. The belly of the helicopter was crushed, rupturing the internal fuel bladders. The helicopter bounced, tumbled, and came to rest facing the opposite direction to the line of flight, approximately 60 feet from the initial point of impact. There were high concentrations of fuel at both the initial impact point and the final resting point of the fuselage, with traces of fuel spills along the wreckage path. An intense, fuel-fed fire consumed most of the helicopter.

Rotor strike marks were found on the gravel and rock surface approximately 10 feet beyond the initial impact point. All five main rotor blades were within the vicinity of the wreckage area. Each main rotor blade ejected outwards from the body of the helicopter and broke in two or three pieces, suggesting that the rotor system was powered at the time of the accident. Most of the cabin area and main fuselage had burned away. There were no main rotor strikes evident on the tail boom or the fuselage. Damage to the tail boom and tail rotor components was due to impact forces. Other components were examined to the degree possible, and no indication of a pre-existing mechanical malfunction was found.

Various fuel samples were gathered from the fuel supply tank where the helicopter was based. All of the samples were clear and bright, with no trace of contamination. The engine (Rolls-Royce Allison 250-C20B) was examined at the TSB Engineering Branch; no pre-existing mechanical failures were found. An examination determined that the engine was delivering power at impact; however, the level of power could not be established.

The aircraft was certified, equipped, and maintained in accordance with existing regulations and approved procedures. The aircraft had flown a total of 7623 hours and had undergone its last 300-hour inspection at 7543 hours. There were no known mechanical deficiencies before the flight. Although precise data was not available, it was estimated that the aircraft was being operated within the prescribed limits for weight and centre of gravity. The pilot was sitting on the left side.

A helicopter can exhibit the descent profile and impact characteristics of this accident for a couple of reasons: vortex ring state or power turbine rpm (N2) droop. Vortex ring state, also commonly referred to as "settling with power", is a condition of flight where the airflow through the main rotor is re-circulated. The result of this condition is that, as power and pitch are increased, the rate of descent also increases. It is generally accepted that three conditions are required for the onset of vortex ring state: zero or near-zero airspeed, powered flight (induced airflow passing downward through the disk, with higher power settings being more critical), and a rate of descent between 300-600 feet per minute. Under these conditions, a helicopter may start to descend rapidly. If a pilot then applies more collective pitch to slow the descent, more rotor downwash is created, which intensifies the re-circulation and increases the rate of descent. To recover from vortex ring state, a helicopter must exit the disturbed column of air that is being produced, either by entering autorotation or by gaining clear undisturbed air by displacing the cyclic forward to regain airspeed. A significant amount of altitude may be lost during a recovery attempt, and recovery at low altitude may not be possible.

Power turbine rpm (N2) droop occurs when engine power is unable to increase as the rotor pitch is increased. When the helicopter is decelerated abruptly, or during a normal deceleration with a sudden updraft, it is possible for the main rotor rpm (NR) to exceed the normal governed speed. When this occurs, the N2 momentarily rises above the normal governed N2 speed. The magnitude of the effect is dependent on the rate of deceleration or the suddenness and intensity of the updraft. If the NR and N2 rise above the selected governed speed, fuel flow to the fuel control unit will automatically be reduced to bring the N2 back down to the selected governed speed.

If the collective is subsequently raised rapidly in an attempt to reduce high rotor speed or arrest a developing sink rate, the NR will decelerate quickly, and the N2 will also droop because the fuel control unit is still on a reduced fuel control schedule. Once below the normal N2 rpm, the governor will signal the fuel control to increase fuel flow; however, there will be a lag before increased fuel flow causes an increase in N2 and NR. During this period, low NR and N2 speed states can result. If the aircraft is close to the ground, it may not be possible to regain sufficient NR to arrest the descent rate. In the most extreme case, droop can be so great as to induce main rotor blade stall.

The pilot had approximately 7000 hours of flying experience on various helicopter types. An autopsy of the pilot did not reveal any physiological condition that may have affected his performance. Toxicology examination was negative for the presence of alcohol, medication, or illegal drugs.


Analysis
The brief radio transmission during the accident sequence suggests that the pilot was not incapacitated prior to impact. The tight descending turn to the right on approach suggests that he had not visually acquired the cache and was responding to verbal cues from the passengers. Had the pilot visually acquired the cache, he would likely have flown a left turn to allow him to keep the cache in sight during much of the manoeuvring and the approach to landing. During a right turn, the pilot's view of the approaching terrain and the cache would have been blocked by the passengers on his right and by the right side of the aircraft. This would have made it difficult to judge the requirement for speed and power adjustments.

The helicopter was developing a substantial amount of power at impact, and main rotor damage was consistent with powered flight. As the helicopter struck the ground without any apparent yaw, it is likely that the tail rotor components were functioning, and that the pilot had directional control. The imprint of the skid tubes at the initial impact point, the immediate rupture of the belly fuel tank and the presence of a large fuel spill all indicate a high rate of descent at impact. The nature of other fuel spills on the ground also suggests that the helicopter struck the ground at a low forward speed.

Light local wind conditions, the slow flight profile, and the rate of descent described in this report were all conducive to the development of a vortex ring state. During its final descent, the helicopter may have encountered a slight downwind as it parallelled a ridge line to the west of the landing area. A slight downwind would be hardly noticeable but would cause a decreased airspeed on final. Decreased airspeed would, in turn, increase the likelihood of vortex ring state developing during the final descent. If vortex ring state developed during the latter stages of the approach, chances of a successful recovery would have been significantly decreased, and the pilot may not have been able to arrest the helicopter's rate of descent.

The aircraft flight profile described immediately prior to the accident was that of a tight, descending and decelerating turn to landing. Large and rapid power changes were likely made during this manoeuvre, and droop on short final may have prevented the pilot from arresting the rate of descent.

[North Shore]

Am I correct that you are speculating vortex ring state as a cause here?

How do you get out of that? Pitch the nose down, and try to gain forward airspeed to fly out of it? Which, in this case, they might not have been able to do because of proximity to the ground..

Whatever the cause, a sad way to go. My condolences to the families involved.

[Ogee]

I'm basically encouraging, within one limitation, helicopter pilots who are more expert than I to offer their insights into this tragedy.

I believe the story is contained within the pink zone and lines on the top picture. I don't believe this was a crippled machine flying around close to the ground in circles before finally crashing. I think that the time frame from all OK to impact was very likely less than 4 seconds.

Personally, I think this machine lost power just before 14th Avenue and the auto was unsuccessful.

I put the vortex ring thing up because certainly the conditions for it occurring were there. The evidence against it is the intact rotor system after the impact. That would indicate little if any power to the disc and high power is a precondition of vortex ring. If the pilot had climbed up a bit on the east to west leg north of 10th to say 200 feet, and his primary inspection interest was the line along 14th, he would have been descending back to line height before he got to 14th. He might have set up a high sink rate and probably would have been below translation, so some of it is there.

But I do think power loss.

As to your question about getting out, yes, lower the nose to fly out and drop the collective a bit to reduce power. Not enough altitude to recover though.

[carholme]

I don't want to get into the speculation game but I will say that any discussion of Vortex Ring State or Settling with Power are wild assumptions at this point. These are very like circumstances but with different entry variables. VRS can catch you completely unaware and will be one of the most frightening events of your flying career, whereas Settling can be an everyday occurrence for longliners who actually use it to their benefit in many cases. Ask Stl who I think has spent many hours on top of a line.
Regardless the accident a/c was a 206 with three people on board and we know nothing about the AUW or any other conditions to warrant speculation about VRS/SWP.

My question, is what it was doing low and slow in a built up area doing power line inspection? Helicopters are used for this type of inspection all across this country. Unless this is an approved operation in BC, I have never seen a helicopter doing this in a downtown core. If it is approved, I doubt it will be for long. Stl would know if it is approved in BC or not.

It was a terrible accident and I sure as hell would not be offering anything to a newspaper at this moment. Their history of knowledge and accuracy about these events is nothing short of sensationalism.

carholme

[Ogee]

I don't know that I'd say the assumptions are "wild" and as I say, its not really my assumption. I just put up what facts can be ascertained at that point. Certainly once those facts are in, its not wild to have a look at the VRS possibility and I'm sure the TSB will be doing the same thing.

Yes, it's pretty weird about that low down circling around right in the middle of town. It will be interesting to see how that is explained, but they didn't just start doing it, they were doing it in the morning as well, so it wasn't just a spur of the moment thing as they were on their way to do the checks between the substations, which would have been pretty well rural flying.

I've already done my work with the newspaper. The reason they use me is so that they DON'T make the kind of reports you rightly complain about and respect the dignity and reputation of one of our brothers who is now gone. This paper does care about accuracy. The reporter listened to what I had to say, asked for where he could get more information on height velocity curves, and talked to Yearwood, who said the same thing I did. It didn't get into cuddawuddashudda. The only thing I might have changed was the term dead man's curve to height velocity, but I guess those are the words Yearwood used.

If you don't offer this sort of insight to the papers, they then do start to make things up and that's what pisses everybody off.

I doubt there will be any more coverage until the TSB report comes out, although a good reporter would continue to be interested in why there was such a discrepancy between the Hydro story and what was actually observed. I mean the only power lines they could have been looking at were just residential lines on wooden poles like you see in the second photo. If you are going to check lines like that with a helicopter in Cranbrook, it would take you two weeks. I would have thought you could to it with a truck, but a Hydro guy did say that what they are looking for is usually up top and can't always be seen by truck.

So if Hydro knew what they were doing was dangerous, and made up the sub to sub story to cover asses, that certainly is a story.

[sky's the limit]

Ogee, Carholm,


As you've both said, I think it's going to be rather difficult to ascertain the cause of this accident quickly, and I think we are all parties who have a vested interest in the results of the investigation.

To address the low over town issue first. We do on occasion fly low over built up areas, but this is covered under Aerial Work for certain applications. I'm not familiar with the job in Cranbrook, or what the B.C. Hydro people were looking at, but I highly doubt that Big Horn would engage in that type of operation were it not 'legal.' Just can't see an experienced operator such as BH exposing themselves in such a high profile manner for a couple hours work - just my feeling on the subject.

As to the accident itself, it sounds like loss of power or a drive train issue, but I really have no information to work with, so I'm hesitant to speculate. Vortex Ring State, OR Settling with power could be possible causes, sure, but looking at the info posted here as well as elsewhere, I just can't see it yet. Have to wait on that.

Settling With Power is something I personally encounter rather frequently in the course of the work we do, but that work is long line stuff, and usually fast at that, I really can't think of a time where I've ever induced it with passengers on board, even downwind in the mountains - this was an experienced pilot who would have certainly been well aware of the situation and conditions surrounding Settling, as well as the recovery. Just a quick point: the nose doesn't have to come down to recover from Settling, you simply need to gain airspeed, and that can be in ANY direction. I personally go sideways much of the time, but we sometimes use Settling as a tool in production longline work and are expecting it. An unexpected onset would of course be rather different. Settling can be induced and recovered from very quickly once you understand it, and the machine you're flying at the time. Some are better than others at getting out quickly.

Vortex Ring State requires a substantial rate of decent to be present, high power, and near zero relative airspeed. I just can't think that an experienced pilot would allow those conditions to occur.

The Height Velocity, or "Deadmans Curve," is something many of us operate in on a daily basis, and it should be understood that this particular chart on most helicopters is NOT in the Limitations section of the flight manual. It is simply a chart that shows where under certain conditions, the aircraft in question was able to be successfully landed after a loss of power over a hard, flat surface by a test pilot. You can actually do better than the "curve" in real life if you're practicing, because the chart allows a 2 second time lag to occur before the test pilot takes action - key words being "practice." In real life, you are going to be AT LEAST 2 seconds, probably more, before responding correctly to an engine out scenario, so the chart may in fact be optimistic in some situations. Being at low alt, with decaying rotor RPM, and the ground coming up fast, is not a pleasant thought, and I can only imagine how hard it would be to make yourself lower that Collective to recover your RPM, especially if you're trying to get over some obstacles such as trees or houses. At the bottom with no Rotor RPM, it's going to be a very hard impact.

I feel terrible for the families of those involved, both in the machine and on the ground, as well as the people at Big Horn Helicopters, and B.C. Hydro. I can only hope that the investigation provides a relatively quick, and thorough explanation of the cause.

stl

[Ogee]

STL. Great post.

I do agree that a quick understanding is vital. Some of the operators around here are pretty worried about the future ramifications for the BC industry at least.

I have seen some pics in which it looks like the engine at least is pretty well intact, or the compressor section anyway.

And I agree about Bighorn. Just can't see it being illegal if they were announcing they were in the city below treetop level a couple of hours before it happened.

Hope so anyways. Otherwise the insurance company might be trying the contrary to the regs get out of paying tactic.

[Plim Sole]

My 2 cents.

Tail Rotor/Gearbox/Shaft Failure. Appears to have take a straight line from top of drop to impact which is unlikely and surely someone would have seen the thing spinning like a top?

Engine Failure/Power Loss - Could well be.

And the curse of all helicopters - wires! So it was flying (very) low alledgedly, over a built up area and lots of wires. Surely a wirestrike (or tree etc) has to be part on the cards here? Clip a wire with a skid, pitches you forward and down, no chance to recover and you arrive at the seen of the accident.

Just a thought, as the grey matter churned over.

My heart felt sympathies to all involved. May each day get a little easier.

[sky's the limit]

So, Kenyans are asking for an "expedited investigation" and compensation.

Thoughts?

stl

[Widow]

Someone "important" on board, high public interest ... grrr, you don't want my thoughts.

Anyway, R.J. Waldron & Co. are involved in the investigation. They'll get to the bottom of it.

[Cat Driver]

So, Kenyans are asking for an "expedited investigation" and compensation.

Thoughts?

STL one must be familiar with the culture of the people involved, in this case TIA.

[sky's the limit]

As I recently found out in another area, many other cultures look for compensation when things like this happen, you need look no further than south of the 49th.... Of course, many others do not, although so far in my experience it has more to do with socio-economic levels than actual culture.

I'm not too keen to see any compensation paid out, unless there is a finding of Gross Negligence as the cause, whether that be maintenance, or piloting. Anything short of that, and I'm not on board with a pay-out.

stl

[Ogee]

I don't think Mr. Otieno understands how these things work in BC.

I did the Coval Air crash in Campbell River back in 84 and remember the lawyers telling me at the time that there would be little compensation, i.e. under $100,000 per victim, because they were all dead and because of the law in BC.

The law is the Family Compensation Act. It arises out of the concept of "duty of care" which is linked with the tort of negligence. The idea is that the air carrier does not owe a duty of care to the survivors and therefore they can't sue for negligence or loss of support, etc. from the deceased. It did owe a duty of care to the deceased. The FCA basically allows a family member to stand in the place of the deceased and sue on his behalf, with the proceeds going to the family as if they were part of his estate.

Mr. Otieno's family may or may not have difficulty in gaining any compensation for his death. The issue is this. In North American culture, there is not an expectation of financial support from children to parents in their old age. That being the case, parents rarely obtain any kind of compensation for the death of a child. However, if the family is from another culture and that culture is such that children do support their parents in their old age, then an award reflecting that may be given.

Don't take that as legal gospel, but I think its close to the general theme of the whole thing. I'm sure though that I haven't covered all aspects of it.

The pilot and the two Hydro men are covered by WorkSafe BC and that is where the only compensation comes from as far as I know. There may be an exception in cases of gross negligence, but I don't think this instance can be described as gross negligence.

Of course the key right now is waiting to hear what the TSB find out in the teardowns, if anything can be found out.

There remain questions as to exactly what kind of operation this was. The observed behavior is inconsistent with the BC Hydro explanation, that is for sure.

The two Hydro employees were from the transmission section of the company, i.e. they were not district linemen. The transmission guys work on 60,000 volts and above lines. Those lines are identifiable by the fact that there are no transformers on the poles and the glass insulators are noticeably bigger. Helicopters do work down low on these lines where they pass through cities and towns and yes, it does piss people off. The problem is there weren't any such lines in this area, or at least that I could see.

Just talked to a lawyer on another matter and this came up. I guess the FCA does not severely restrict compensation as this guy had gotten 10 million in damages from a helicopter crash about 20 years ago.

[sky's the limit]

Very interesting.

Thanks Ogee.

stl

[BoostedNihilist]

Can't they just sue the hull insurance provider?

Is it not like car liability, where, if you are involved with an accident with a pedestrian, you are at fault no matter what the causation? One thing is for sure.. mr otieno certainly did not cause the craft to fall out of there air onto him.

Those people who were in the aircraft for sure were aware of the potential hazards associated with the flight, but mr. otieno was simply walking down the street, not a party to any facet of the operation above. It was a freak accident yes, but the family members of mr otieno definitely deserve compensation, definitely more than 100k.

[Ogee]

Can't they just sue the hull insurance provider?

Is it not like car liability, where, if you are involved with an accident with a pedestrian, you are at fault no matter what the causation? One thing is for sure.. mr otieno certainly did not cause the craft to fall out of there air onto him.

Those people who were in the aircraft for sure were aware of the potential hazards associated with the flight, but mr. otieno was simply walking down the street, not a party to any facet of the operation above. It was a freak accident yes, but the family members of mr otieno definitely deserve compensation, definitely more than 100k.

BN

I'd say there are possibly two or three targets for lawsuits. Whether or not they have done anything wrong, Bighorn will be a target, so they get sued and their insurer pays out if they lose. Hydro may find itself being sued as the instigator of these type of flights, and Transport may get their name on the writ for allowing it.

I guess the issue is, would a reasonable man be aware there was an inherent danger in this type of flight operation and did he take reasonable steps to prevent what happened and did failing to take those steps result in the harm done.

Don't have an opinion one way or the other. Much more facts needed, but I will say that although the results were horrible, I don't see that anybody behaved horribly in all of this. Something happened at the worst possible time with the worst possible result.

I'd actually be surprised if this went to court. Honorable people would pay where payment is due and we could all learn and move on. But who knows?

[sky's the limit]

The words "honorable," "people," and "pay," are unfortunately rarely compatible....

I hope it doesn't get ugly, that's just not helpful in the healing process for anyone.

stl

[Widow]

BC Hydro changes chopper policy after crash that claimed four lives on B.C. street
1 hour ago

VANCOUVER, B.C. — BC Hydro has a new helicopter-use policy in place after a fiery crash killed four people in Cranbrook, B.C., last year.

After a safety audit, Hydro has directed that it will be using twin-engine helicopters in most of its operations.

Two Hydro employees, the pilot of the helicopter and a pedestrian were killed when the chopper crashed onto a Cranbrook street and burst into flames in May of last year.

Susan Danard of BC Hydro says the twin engine choppers will be used for low flight or inspection work to improve safety.

Bill Yearwood of the Transportation Safety Board says the board suggested to Hydro during its safety audit that a multi-engine helicopter would give a better safety margin.

The cause of the accident hasn't been determined, but Yearwood says they've ruled out most other systems except the fuel system.

http://www.google.com/hostednews/canadi ... Orwyvo8FJ3A

[freakonature]

Thank's Widow. I was looking all over for that.

[r22captain]

Glad to see multi engine is catching on. But unfortunate it took an even such as this.

Be interesting to see who will be doing the work and with what machine.

[freakonature]

So is this just a knee jerk reaction? Or should all aircraft have two engine's to be considered safe? A company of this size make's a big statement when they impliment policy's like this. The tricle down effect can go in many direction's.

[sky's the limit]

So is this just a knee jerk reaction? Or should all aircraft have two engine's to be considered safe? A company of this size make's a big statement when they impliment policy's like this. The tricle down effect can go in many direction's.

Yes,

And that direction is negative. Notice how it doesn't say "all" operations? I think you'll find the increased tariff's and reduced availability will have them wiggling out of the twin stuff for many/most applications.

stl

[The Mole]

What are the requirement to fly low level in a built up area...........hmmmmm

twin engine and a low fly permit. It took 4 deaths for hydro to recognize rules that are already in place.

You can't prevent everything but you can reduce the risk.

[r22captain]

please point out the multi engin requirment for me

722.22 Built up Area and Aerial Work Zone

(1) For air operator authority to operate an aircraft over a built up area at altitudes and distances less than those specified in Section 602.14 of the Canadian Aviation Regulations, or to conduct a take-off, approach or landing within the built-up area of a city or town, an aerial work zone plan shall be submitted to the Transport Canada Aviation Regional Office in the region in which the flights are to take place at least five working days in advance of the operation and include:
(amended 2005/06/01; previous version)

(a) certification that the governing municipality has been informed of the proposed operation;
(amended 1998/09/01; previous version)

(b) purpose of the flights;

(c) dates, alternate dates and proposed time of day of the operation;

(d) location of the operation;

(e) type of aircraft to be used;

(f) altitudes and routes to be used depicted on a map of the area;

(g) procedures and precautions to be taken to ensure that no hazard is created to persons or property on the surface including locations of forced landing areas in the event of an emergency; and
(amended 1998/09/01; no previous version)

(h) name of the responsible air operator person to contact.