Need a reason for a helicopter crash

Certainly in the cold if the fuel is contaminated with some water it can cause the fuel line to freeze, causing a gradual drop in power. That would be a relatively easy crash-landing for an experienced pilot.

Bad weather could also force them down, but unless it's a surprise storm they really should have been aware of the risk before setting out.

Hallen is my chopper go-to guy. I hope he's flying nearby and lands to lend an always helpful hand.

Depends on how isolated it is. A helicopter could fly far enough to be out of radio range of the airport, especially with mountain interference. They would have likely left a flight-plan at the airport though, I don't know if that's significant or not.

A brownout. When flying very low, the rotor causes a downwash of terrain particle up in the air. Happens often over soft-particle landing sites - like in the desert - as the engine loses power when it sucks them in.

Could be in your case that the pilot thought about landing on a snow-covered flat but didn't know about the sand-like nature of the soil underneath it. A dense cloud formed and the engine cut off, sending it fifteen feet down in a free fall. Survivable for occupants fastened to their seats, but enough for a rotor blade to shatter on impact.

-cb

Bad weather can sneak up you faster than you think. A couple of years ago, the town where I work got invaded by a group of National Guardsmen in Black Hawks (5 helicopters and 43 guys). It was an unusual event. Well, the landing was unusual; rapid weather changes are pretty typical.

From the local paper:

http://www.yankton.net/articles/2009/10/06/community/doc4acaccb00489a500704681.txt


The Yankton landing marked the end of a challenging day in the skies for the North Dakotans. As night approached, the unit chose to land after an 8-hour flight

The trip was complicated by the fact that the rainy, cloudy, windy weather was not forecast prior to takeoff, Larsen said."We took off this morning from Bismarck, around 10 a.m. The forecast said we could do everything we intended to do," he said.

"Unfortunately, we ran into a low ceiling and low visibility. A half-hour out of Bismarck, the forecast said that things would get better in this particular area (up ahead), then this particular area.

"But the weather has been bad everywhere we turned. By now, we should be in Stillwater, Okla."The crew members wanted to push ahead on the mission, meeting the timeline for arriving at Fort Sill. But they also realized the safety hazards produced by the rainy weather and falling temperatures.

"We could have picked up icing," Larsen said. "We were restricted and couldn’t go into the clouds."The helicopter unit turned to its Global Positioning System (GPS) to determine possible landing sites. The decision was made to land at Yankton.

A realistic scenario could be a bird strike. A bird ingested into the engine would cause an engine failure, forcing the pilot to make an emergency landing. The technique is called "autorotation," and it's something helicopter pilots practice.

The pilot has few options about where to land in an autorotation. It's a steep descent with a flair at the end. They could walk away if they were lucky enough to be flying over an area clear of trees and fairly level.

Hope that helps.

I'd say bad weather - sudden, unexpected bad weather - is a good bet. When we have a crash around here (very, very rare) that's usually the cause. A sudden cold squall, or a downdraft, shift in wind direction, etc.

debirlfan said:

Yes, the pilot is very good, and isn't about to fly into bad weather, however there is an important reason for making the trip, so she'd be willing to stretch it a bit more than she would for a sightseeing run or the like.

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Then she isn't a good pilot. A "good" pilot won't knowingly push it beyond her limits or those of the aircraft because of some "important reason." Other than life-or-death, no reason is that important.

About water in the fuel freezing up. Water in the fuel will stop an engine irrespective of the temperature. Water doesn't burn. It usually happens shortly after takeoff. Being heavier than fuel, the water is at the bottom of the tank and gets into the system first. A good pilot always checks for and eliminates water in the fuel tank before taking off if the craft has been sitting for a while since the last flight. Any pilot who takes off with water in the fuel is not a "good" pilot.

Your best bet is a mechanical failure resulting in autorotation and no place to put her down. You don't need to go into details and probably shouldn't unless your ms is vetted by a pilot experienced in the type aircraft you use.

Running out of fuel is a remote possibility. That's what killed Gary Francis Powers.

ETA: Birds don't usually get sucked into engines other than jets. A bird strike would have to hit the rotor, and survival would be unlikely. Weather isn't as big a problem in a helicopter. Low visibility? Hover and figure your options. You stay out of thunderstorms, too.

Actually, that's a very good point Al Stevens made. Just have lights flashing and emergency warning beeps. The pilot has to autorotate to bring 'er down.

How would they really ever know what had happened? I mean weeks or months later after the FAA investigation they might find out, but in the context of the story, what does it really matter what went wrong?

Helicopters have even heavier maintenance requirements than airplanes.

Fuel and oil lines should not break without intent. But metallic components do, on occasion, fail catastrophically (without prior indication). I suppose an oil pump failure could lead to a rapid engine failure.

Without mechanical failure or pilot error, you don't have a crash. ;-)
Al has covered it pretty well.

Depends a bit on the type of helicopter it is. Engine failures do happen, but might seem a bit convenient. Weather can force you down, but then you just wait and take off again when it clears.

No, another airplane isn't going to be able to force them down.

The bad guys can do all kinds of mean little things that could break the helicopter. Gunk in the fuel can clog up the injectors. Or, a small bomb could easily take out a fuel line, or a hunk of metal loosely attached to the intake (behind the filters) could break loose and destroy the engine (turbine engine). This last one is pretty cool in that it would be very difficult for a crash investigation to figure out, where a bomb would be more obvious. If they plan for it to happen an hour after takeoff when the helicopter is over rugged terrain, they're probably going to be pretty sure it will kill the crew.

Once the engine has failed, the pilot will have to autorotate (assuming it's a single engine helicopter). The pilot has one shot to set it down safely and won't have time to pick a convenient spot to land. Whatever is close will have to work which means that most likely, the helicopter will get bent. If you do it right, everybody walks away, but it will be a pretty hard landing.

What type of helicopter?

If it's a jet turbine-powered helo, the turbine could suck in a bird or something like that. Most higher-end helos are turbine-powered. Though I have no idea how they could ingest a bird...

Mark G said:

What type of helicopter?

If it's a jet turbine-powered helo, the turbine could suck in a bird or something like that. Most higher-end helos are turbine-powered. Though I have no idea how they could ingest a bird...

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They really can't. Helicopters work in harsh environments, often close to the ground. Also, because of the rotor wash, they kick up a lot of junk when landing. All turbine helicopters have screens and other systems to keep dirt out of the engines. Birds aren't going to get through.

Our air ambulance flew into high tension cables. However, everybody died. So maybe that isn't the best idea.

Some kind of failure to the tail rotor?

The windward or downslope side of a mountain could cause an immediate downward force because of the wind wash, causing the helicopter to suddenly lose altitude and either stall, or impact the ground without gaining altitude, even at full throttle.

Was it a Steve Fawcett, or some guy, who had this happen to him a while back? He hit a tremendous downdraft while flying over a range of mountains. His craft was literally pulled into the canyon floor.

Tri

Hallen said:

They really can't. Helicopters work in harsh environments, often close to the ground. Also, because of the rotor wash, they kick up a lot of junk when landing. All turbine helicopters have screens and other systems to keep dirt out of the engines. Birds aren't going to get through.

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That's what I thought. I was trying to think of a turbine-powered helo that had unshielded intakes, but I thought maybe...

triceretops said:

He hit a tremendous downdraft while flying over a range of mountains. His craft was literally pulled into the canyon floor.

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Pulled to the canyon floor is a little hard to believe. Downdrafts don't do that because air doesn't sink into the ground. It burbles and turns into adjacent updrafts. Reporters often get such details wrong when they write about aviation accidents.

Somebody said:

Some kind of failure to the tail rotor?

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About the tail rotor. Don't screw with the tail rotor. It keeps you pointed in the right direction. Lose it, and you lose control. The bird spins erratically on its horizontal axis. A safe touchdown is virtually impossible. Like this:

http://www.youtube.com/watch?v=hnK9bGCvYtU

Al Stevens said:

About the tail rotor. Don't screw with the tail rotor. It keeps you pointed in the right direction. Lose it, and you lose control. The bird spins erratically on its horizontal axis. A safe touchdown is virtually impossible. Like this:

http://www.youtube.com/watch?v=hnK9bGCvYtU

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Or just watch "Black Hawk Down"

triceretops said:

The windward or downslope side of a mountain could cause an immediate downward force because of the wind wash, causing the helicopter to suddenly lose altitude and either stall, or impact the ground without gaining altitude, even at full throttle.

Tri

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Yes, mountain waves can be powerful enough to put you into such a downdraft that the aircraft does not have the power to fly out of it. They usually occur in extreme mountainous areas when strong weather patterns are in existence. They are somewhat rare and can mostly be avoided by staying above the ridge lines.

Al Stevens said:

About the tail rotor. Don't screw with the tail rotor. It keeps you pointed in the right direction. Lose it, and you lose control. The bird spins erratically on its horizontal axis. A safe touchdown is virtually impossible. Like this:
http://www.youtube.com/watch?v=hnK9bGCvYtU

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At a hover or slow speeds, yes, it's ugly. Chop the power and try for an autorotation is about your only bet (it's an anti-torque rotor and if you remove the torque -- the engine turning the main rotor -- then the spin will stop). Also, if you have some forward airspeed, about 30-50ktis, you can continue flying, try to find a long flat space and then land a bit like an airplane maintaining forward airspeed. It's tricky, but doable.