Flying in freezing rain

[touchdownjm]

How long can a helicopter sustain flight while flying through freezing rain? Also, will it cause the rotor blades to stop, or will they continue to rotate? Thanks in advance

[lelebebbel]

There are very few helicopters that are certified for flight in known icing conditions, so legally the answer is 0 minutes for most machines.

 

As for what would happen if you did it in a machine with no icing protection, depending on how bad the freezing rain is, it would slowly or quickly lose lift and begin to descend. Pieces of ice would likely break off asymmetrically leading to severe vibrations which could also damage things. The blades wouldn't stop unless the pilot ignores warning horns, gauges, and lights, and continues to raise collective until the the rotor stalls out, which would lead to various kinds of structural failure.

 

Ice typically forms first on the airframe such as the tips of the skids because the blades are usually a few degrees warmer due to their high airspeed.

 

Here is a video of a helicopter picking up what I would describe as freezing fog during a landing on a mountain ridge:

It is edited so it is hard to tell how long it took for the blades to pick up that much ice, but it couldn't have been longer than a few minutes.

[TomPPL]

That was one totally amazing video..!

 

I've never seen a helicopter nosed into a mountain like that...

[F224]

I flew for Northwest Airlines for 20 years before a neck injury forced me o retire early. Even with the best anti/deice equipped airplanes Boeing and McDonald Douglas can build, we don't operate in freezing rain, it overwhelms the systems too quickly.

 

Other than climb and decent, we avoided icing conditions as much as possible. Freezing rain has killed way too many people, it would be even worse in a helicopter.

[BH206L3]

You really want to be someplace else, like on the ground in a hanger drinking coffee or over at the Waffle House for some eggs what have you. You avoid freezing rain and icing in general. This stuff will kill you in a blink of an eye. Blaser's Rule by the way Dave.

[Synixman]

I fly 60s in the Navy and we have blade deice. Our flight manual prohibits us from flying into forecast trace or light icing. As a general rule, we avoid icing (visible moisture and less than 4C) like the plague. If we were IFR and temps started to drop, we'd request a descent to VFR or warmer temps immediately.

 

In general, ice is going to form on right angle airframe surfaces, not on the rotors first. When we kick on blade deice, it's going to try to symmetrically shed the ice and not into the tail rotor. Oh, and you'll be adding hundreds of pounds in ice weight and might quickly run out of power. All the while we are pumping bleed air into the engine inlet to prevent the compressor from icing. Again, bad things.

 

Preflight planning will get you 95% of the way there. Then, just fly smart. Icing in a helicopter is an emergency.

[Wally]

How long can a helicopter sustain flight while flying through freezing rain? Also, will it cause the rotor blades to stop, or will they continue to rotate? Thanks in advance

 

There's no reliable method of predicting endurance in freezing rain, a few seconds or many minutes (Rosewood). Avoid it like death, because it could crash your helo in a few seconds, or not at all.

 

If the blades ice, they become less efficient, taking more and more pitch and engine power to maintain altitude and control. That process could result in being unable to maintain flight, or a stall with roll and/or pitch excursions. Finally, the rotor shed ice asymetrically and develop damaging vibrations with the imbalance and blade track. If that wasn't enough fun, rotor might shed ice into the vertical fins and tail rotor....

Edited April 15, 2013 by Wally

[iChris]

How long can a helicopter sustain flight while flying through freezing rain? Also, will it cause the rotor blades to stop, or will they continue to rotate? Thanks in advance

 

Unpredictably, with respect to an aircraft not equipped for icing. Ice and snow can accumulate in a way that is not easily predicted. As stated above icing often starts at the airframe. Ice and snow were involved in the Sikorsky accident below:

 

“The loss of power in both engines due to the ingestion of ice and snow. Also causal was the pilot's preflight and in-flight decisions to fly into areas of known and forecast moderate icing conditions in contravention to the prohibitions contained in the helicopter's Federal Aviation Administration approved Type Certificate Data sheet. A factor in the accident was the failure of the company maintenance organization to install the optional ice/snow deflector shields in front of the engine inlets that are designed to prevent the ingestion of ice and snow. An additional factor was the inaccurate and inappropriate weather briefing provided by the second AFSS specialist.”

 

“The anti-ice/deice systems on the helicopter consist of a combination of electrically and bleed air heated elements protecting the windshield, the oil tank mounting ring, engine air intake ducts, engine inlet guide vanes, starter cover, and the front frame of each engine. The systems are pilot controlled and automatically regulated to prevent ice from forming. The system includes cockpit control switches for the systems and advisory and caution lights to alert pilots to the operational status of each component."

 

“In addition to the above described anti-ice systems, an engine inlet ice deflector shield can be installed in front of the engine inlets to prevent any accumulation of ice and snow that forms around the upper deck and mast area ahead of the engines from entering the engine inlets. According to Croman Corporation Director of Maintenance and the subsequent examination of the wreckage, the engine inlet ice deflector shields were not installed.”

 

Aircraft: Croman Corporation SH-3H, registration: N612CK

Edited April 15, 2013 by iChris

[avbug]

Icing is nothing with which to trifle.

 

I've done atmospheric research flying, including considerable flight in icing conditions. A project to which I was assigned not too many years ago involved operating a learjet into thunderstorms. We sought out the areas of maximum icing for various reasons, to enter the storms. This was usually the -5 to -15 C range, and we often picked up 3" or more of ice.

 

I've been in icing conditions on many occasions in which I picked up ice very rapidly, even to the point of having altered flight characteristics. I've had ice horns built of airfoils that have been 6-8 inches growing off the upper and lower leading edges of the airfoil, into the slipstream.

 

Ice is a funny thing. It can be deadly to one aircraft and yet not affect another nearby, especially in cases of freezing rain. Fly through the right spot and through the rain, and it can quickly exceed the capabilities of the ice protection or that of the aircraft: the definition of severe icing.

 

I've flown aircraft in ice with no ice protection, with boots, hot leading edges and intakes (electric and bleed), and other means of protection, and it's important to note that none of those systems have capability beyond light to moderate icing, and are meant at best to get one through the ice, but not to stay in it.

 

Freezing rain has the capability of producing rapid buildups of ice that not only alter the shape of the airfoil, but which add weight to the aircraft. In small droplet conditions, ice forms on small surfaces first; thin airfoils, probes, etc. In supercooled large droplet conditions, it forms on everything, and runback over airfoils (such as a rotor) can change the airflow dynamics by altering the airfoil shape and laminar flow. With any icing laminar disruption occurs, leading to 25% or more loss of lift in the airfoil, as well as a change in the center of lift and center of pressure on the airfoil. On a spinning airfoil such as a main or tail rotor (propeller, etc), it can lead to harmonic issues, and imbalance. Ice doesn't shed evenly, if it sheds, and that leads to uneven loading of the spinning disc with variations in lift, sometimes noticeable vibration, and so on.

 

In an airplane, one sometimes has the option of climbing or descending to get out of icing conditions. Outclimbing them in a helicopter is usually not an option, and given the lower altitudes flown, so is descending. It's said that icing extends through only a narrow altitude band, but that's also some very dangerous counsel, as it can extend right to the surface, and can extend to very high altitudes (I've encountered it well up into the flight levels).

 

Don't count on being able to shed ice if you get it; you need to get out of icing conditions quickly. Land if you need to. Avoid ice, and get out if you find it.

 

Take ice very, very seriously. It's possible at temperatures above freezing (generally accepted up to about +5 C, down to about -15C for ideal conditions. It can exist to -40 F/C. It can exist outside of storms, where it falls free of the cell, and it can exist beneath cells, in cloud, and outside of the cloud in precipitation. It occurs in fog and ice fog. One of my assignments many years ago involved treating freezing fog to increase visibility, using dry ice dispensed from aircraft. it worked very well, but we were also constantly in the ice and constantly picking up ice. Ice can quickly go from handled to excessive, and at that point, it may be too late. Plan carefully to avoid ice, and don't underestimate it's effect on your aircraft and performance.

[Nearly Retired]

Someone comes on this forum and in his first post he asks a question: How long can a helicopter sustain flight while flying through freezing rain? It's kind of a troll-y question, no? Maybe the questioner is an author researching stuff for a book - that's what first crossed my mind. He's got a scenario in which a helicopter is making a daring escape from somewhere and of course it's horrible weather and they encounter some killer freezing rain and...

 

And then the "experts" come on and give him the book stuff about how a helicopter will explode at the first sign of ice. Obviously, some people who post here have never flown a helicopter in freezing rain before. I, on the other hand, have been that unlucky. My first flying jobs were in NYC and we flew year-round. Yes, in winter too. Contrary to popular belief, helicopters do not fall out of the sky at the first encounter with ice. They don't "stall", spiral out of control or shake themselves apart. They just get coated with ice. The long-term ramifications will depend on how long you want to stick around in the freezing rain.

 

So wait...are we talking about a helicopter flying in the clouds up at altitude on an IFR flight plan? Or are we talking about a VFR helicopter operating "down in the dirt" (where we usually fly) that happens to encounter an area of freezing rain?

 

In the winter, a cold, rainy day can quickly turn into a snowy day. Alternatively it can quickly turn into a freezing-rain day. You just never know. You can't shut down operations just because it's 33 or 34 degrees out and raining and supposed to snow later. You do what we do: You keep flying until you can't.

 

On such a day, maybe you're slogging along in rain when the windshield starts to ice over. "Damn." (Remember, you're going to be flying extra-low because freezing rain implies crummy weather - low ceilings and low vis.) You look out at the skids and see the leading edge of them covered in ice. "Double-damn." Up in New York our flights were not very long, so we didn't spend a whole lot of time cruising along in freezing rain. Once the windscreen ices over you can't see anyway, so pressing on is kind of dumb. So windshield ice becomes the limiting factor. Helicopter typically don't have good defrosters like cars do, and our bubbles aren't heated.

 

On the other hand, turning around isn't always an option if you're close to your destination than departure point. So you continue, all the while being extra-cautious (too late now!) and ready to set the thing down at a moment's notice...like, if the forward visibility really goes away. Thankfully, the engine is probably not going to flame out if you've got snow baffles and engine anti-ice on.

 

In a helicopter powered by a turbine engine, the main rotor blades will not pick up much ice in cruise flight. Engine exhaust will keep the outer part of the disk clear. That Astar in the video above obviously picked up all of his blade ice as he sat there idling in the ice-fog on the peak. (VFR helicopters don't typically cruise along in ice fog where the visibility is zero.)

 

Same for the tail rotor, which sits directly in the exhaust of the engine(s). Tail rotors don't generally ice up - again, not in turbine helicopters. Your R-44 ice-mileage may vary.

 

Now, the inboard parts of the main rotor blades and the hub will ice up. I've landed with quite a lot of ice on the rotor head, blade grips, and push-pull tubes. I've landed with the skids iced-over so badly that I slipped on the step attached to the crosstube and fell on my ass. I've landed with so much ice on the helicopter that I've looked at it and gone, "Damn! That was stupid! I won't do that a third time!"

 

When I was a kid I used to fly with a guy who did traffic-reporting in a Bell 47. Some days we'd be flying along in really, really, really crappy weather...why, I don't know. It was back in the days before remote traffic cameras and people calling in accidents and tie-ups from cell phones. The wooden blades on that 47 would ice up and start shaking. The pilot would give the stick a couple of quick sideways yanks and the vibration would go away - for a while. We'd land when the ice accumulating on the front of the bubble would get so bad he couldn't see. The hub and stabilizer bar assembly would be covered in ice. It was exciting! Then again, I was 13. I was lucky that when I started flying for a living, piston-engine helicopters were becoming a thing of the past.

 

Again, we're talking VFR (visual) operations here. When you start to pick up ice you know you're not going very far from there (unless you fly back into a slightly warmer area and the ice melts off - which I've had happen too). But if you fly a helicopter up in the clouds (IFR) and pick up a load of ice, well, you done screwed the pooch big time, bub. Because then all of that bookwork theory comes into play.

[avbug]

Someone comes on this forum and in his first post he asks a question: How long can a helicopter sustain flight while flying through freezing rain? It's kind of a troll-y question, no?

 

That was my first impression, but it may have been an innocent question, too.

 

A chief pilot once asked a group of pilots in a seasonal ground school "Who knows how much ice the Commander can carry?" I thought at the time it was a stupid question, but gave him the benefit of the doubt, hoping he had a point. It turned out that he didn't. "The Shrike can carry all the ice you can put on it, and it will only lose 15 knots."

 

He was an experienced hand in the Shrike Commander, and I hadn't flown it in ice. As it turned out, we had to drop some folks in Phoenix, so off we went, and closer to sunset, we headed back Approaching the Mogollon Rim, an area of rising, mountainous terrain, we began to pick up ice. We were unable to climb to the MEA, and gained a little over an inch in 60 seconds. The aircraft ahead, and the aircraft behind reported no ice. Airspeed decreased rapidly as we tried to maintain altitude. We started about 180 on the speed, then went through 120 at blueline (best rate of climb, single engine), best angle of climb, and we were still descending.

 

Ice was coming off the props and striking the fuselage. It sounded like two people sitting behind us constantly firing 12 gauge shotguns. We ended up continuing in that descent, unable to go anywhere due to terrain and the descent itself, until we were in solid fog and cloud; we made contact with cars on a road on their way from a paper mill. Recognizing the mill, we followed the cars and road into Taylor, AZ. There we landed. It wasn't until daylight the next day that we found holes knocked in both sides of the airplane, from the ice.

 

A few days after that, I was standing next to the Chief PIlot who told someone again, "The Shrike can take all the ice you can throw at it and it will only lose 15 knots. Isn't that right?" He asked me.

 

"Well," I replied, I know it will lose 50 knots in a minute..."

 

Guessing games as to how much ice an airframe could take are very dangerous.

 

The only answer should be "no more than I can possibly help."

[Nearly Retired]

Well maybe in ground school the Chief Pilot actually said "50 knots" and you heard "15."

 

I've done that. Hot-loading on an oil rig can lead to this confusion.

 

Me: "How much does that toolbox weigh, Mr. Roustabout?"

Rigape: "Fifty-een pounds, Mr. Skygod."

Me: "Load up!"

 

P.S. Love the Shrike

[touchdownjm]

The questions was asked since I was curious about the details of the crash that occured in Alaska with the State troopers. Here is a link to the article from the the Anchorage paper with the latest.

 

http://www.adn.com/2013/04/10/2859248/few-details-revealed-in-helicopter.html#storylink=misearch

 

 

[iChris]

The questions was asked since I was curious about the details of the crash that occured in Alaska with the State troopers. Here is a link to the article from the the Anchorage paper with the latest.

 

http://www.adn.com/2013/04/10/2859248/few-details-revealed-in-helicopter.html#storylink=misearch

 

The Alaska State Troopers have had at least one prior officer die in a helicopter crash during a search and rescue mission. Trooper John David Stimson was on a chartered helicopter (Bell 206) in 1983 that was attempting to reach a downed pilot in a blizzard. The chartered helicopter crashed near Cordova. Ice was an issue.

 

Accident occurred Thursday, January 13, 1983 in CORDOVA, AK Aircraft: BELL 206B, registration: N74PR

Edited April 16, 2013 by iChris

[Nearly Retired]

The latest article in the Alaska Daily News does not mention freezing rain. However, reports do mention "light snow" and sure enough, light snow can turn to freezing rain. But it seems like the snow was tapering off at that time, and the ceiling and visibility were...I wouldn't say "great" for a flight but the conditions were at least not horrible at Talkeetna. But it was nighttime and helicopters are very, very easy to crash. With all the flight recording equipment installed in that helicopter, we'll have a pretty good idea of what happened soon enough without having to speculate on it in the meantime.

[ridethisbike]

Very true. I'm kind of surprised that they even had those particular recording capabilities. My understanding is that it's not common practice throughout the industry...