Helicopter Icing Limitations

[helopat]

Gents,

Getting awfully tired of "who's paying better" and "who forged what licences" discussions...I still read them avidly. Just though I'd throw this one out there for a bit of a fresh discussion.

I'm currently flying Seahawks for the RAN and used to fly for the USN (same acft type). If our blade de-ice (main and tail rotor), windscreen de-ice, or engine anti ice is not functional, we are limited to temperatures above +5degC in visible moisture. If we've got all the functional de-ice and anti-ice kit, we can operate down to +1degC in visible moisture.

Anyone else want to weigh in with their aircraft types and similar limitations? Stories of terrifying ice build up:eek: and 'derring do' ;) in escaping to tell the tale?

Except for one instance of snow flakes coming out of the air conditioning ducts at 10,000' in Southern California, I've been extremely lucky on the icing front.

HP sends

[whatsarunway]

Yeah, I get hail stones coming from the air con ducts when i fly through cloud with the heat on! Whats that all about?:confused:

[rotordude]

Helopat.
You wrote: If we've got all the functional de-ice and anti-ice kit, we can operate down to +1degC in visible moisture.

Why would you need main & tail rotor de-ice at +1degC?

rotordude

[helopat]

Why would you need main & tail rotor de-ice at +1degC?
rotordude

Mate, for the same reason you need it for your engines and windscreen. Whirling wings of death=lower pressure=slight reduction of temperature (same as at the engine intake)...add visible moisture and, even with slightly plus temperatures, you can get icing. Admittedly its not likely, but thats the way the regs are written for the Seahawk at the moment.

So, what I was really after is what the rules are for OTHER people (ie. you)...care to say? I mean, you're the guy from Norway so I assume you have more flight in icing (or potentially icing) conditions.

HP

[IHL]

Helopat wrote"If we've got all the functional de-ice and anti-ice kit, we can operate down to +1degC in visible moisture."

That must be a typo , with all the de-ice and anti-ice functional you must be able to operate at temperatures well below freezing.

It has been my experience-with the exception of engine icing- that you don't pick up ice in visible moisture if the temperature is +0.1 C. I have never picked up icing flying in snow at temperatures below 0 either.

[skadi]

As far as I remember, the Westland Seaking could be flown under light icing conditions without any deice-devices except heated windshields.

[Gomer Pylot]

MR & TR blades are among the last places you'll get ice, because they're being warmed by moving through the air at very high speeds, sometimes near the speed of sound. Feel the blades sometime immediately after shutting down, and you'll find they're very warm. The extreme inboard portions, though, aren't moving that fast and can get ice.

As for what temperatures you can fly in with what equipment, that is in the limitations section of the RFM, or in your Ops Specs.

[ShyTorque]

I think it's a mistake to try to give a "one size fits all" answer regarding exact temperatures because different types are affected differently.

Torque increases can be a good indication that ice is building on the main rotor system. Irrespective of ice build up on the blades themselves, build up on the rotor control system such as pitch rod ends or servo valve links might be more critical (the latter is a check to be carried out on the S-76 before flight in low temperatures).

[rotordude]

Gomer Pylot is right!

Anyway, in order to get back on track:
AS 332 "Super Puma".

MR & TR (Redundant, two systems for both MR & TR):
Both systems operational - Intentional flight in FZRA prohibited.
One system u/s - Maximum flight time in icing 15 min.
Both systems u/s - Avoid icing conditions

Inlets and Windows u/s (according to MEL):
Avoid visible moisture below +5 degC.

Worst experience I´ve had is not due to icing itself, but due to static discharges when flying through dry snow in -10 to -15 degC. Two of three windshields cracked and one alternator went offline.

[helopat]

IHL, nope, no typo...like it or not, thats the way its written for us at the moment. However...

As far as I remember, the Westland Seaking could be flown under light icing conditions without any deice-devices except heated windshields.

Meester Skadi (nearly) hits the nail on the head. With the Seahawk we're supposed to be able to fly in trace or light icing...trouble is we don't have any way of measuring ice accretion (accretion meter)..so really a meaningless statement in the flight manual...however, accretion meter is something thats in the works.

Cheers for all the input.

HP

[malabo]

Bizarre limitations you have in the Seahawk and 332. Maybe just a feature of that helicopter but nothing like anything else I've flown. Most blades run hot, up to plus 6C at the tips, so normally nobody worries much about ice until down to about -4. Even then, as Shy Torque puts it, all we ever watched was the torque - icing up meant the torque increased. And it practically never happened, otherwise you wouldn't have a helicopter industry in Canada. Even those of us that went looking for ice would take off day after night in +2C drizzle and climb, sleet at 1000' snow at 2000' dryer snow at 4000'. The 212 and 222 could carry a whack of ice, 412 and 76 not so much, but it was a rare event anyway. Night IFR slinging in the Arctic in the winter - sometimes -30, sometimes -20, if it got warm then -10.

Icing tests just might be some kind of sick joke. "Yep, we flew through a cloud at -1 and didn't pick up ice so we know the anti-icing system works". Chances are that if you tried it for ten years without anti-ice you'd never have picked any up anyway. Watch an operator in Canada like Helijet with their S76 flogging around in moisture below freezing all day every day with 12 passengers in the back, or Cougar and CHC doing the same off the east coast. They know more about ice that anyone that turns tail at +5 (no offense, I know you are simply complying with an RFM limitation).

BTW, yes I have picked up ice on a few occasions. Very few, and in very specific conditions. And no it didn't stop me from flying into a cold cloud the next time.

malabo

[rotordude]

Night IFR slinging in the Arctic in the winter
malabo
Sounds interesting!

[FloaterNorthWest]

If my memory serves me right the Lynx Mk 1/5/7/9 was 20mm glaze ice or 60mm rime ice on the ice accretion gauge (which went up to 50mm) or an increase of 25% torque on bottom engines, you then had to vacate icing conditions.

I'm sure Mighty Gem will have the exact figures to hand. ;)

FNW

[oryxs]

Gomer Pylot

Have to disagree with you on the blades being the last place to ice up. I operate in it about 6 months of the year and have seen no ice on the machine(mirrors/door handles etc.) and the tq going through the roof and vice versa. Everything else(mirrors/door handles etc.) iced up and no tq rise. I would agree that the temp of the blades most probably played a role in this but be careful with ice. Thats what makes it so unpredictable. I can post some pics if you guys are interested in seeing machines with 2 inches of ice and still working as advertized.

Rotordude

The AS332 RFM also includes frz drizzle now. This was changed about 3 years ago. Used to operate in it but not anymore

[R22DRIVER]

Lets see your piccies!

[[email protected]]

The Sea King is cleared to minus 7 degrees C in icing conditions up to a maximum of 3000' DA (subject to weight). We have EAPS/SNIPS (Engine air particle seperator/snow and ice protection system) which is a big box in front of the intakes with scavenge/eductor fans to clear the plenum chamber (inside the box). There is engine anti icing (hot oil and combustion chamber air) for the front frame of the engine and pitot head heating. We have a Tq rise limit and a cruise guide indicator limit for icing encounters and although there is an ice accretion probe fitted there are no limits published.

As far as our definitions go you are not in airframe icing conditions until you are below 0 deg true with visibility below 1000m due to water vapour which does make helopats icing clearance rather odd. Our engine icing conditions are defined as below plus 10 deg in rain or cloud.

We are not allowed to fly in freezing rain or drizzle (seen it once and that was scary)

The rotor tips are the last things to ice up because of kinetic heating (IIRC it is the square root of the airspeed that gives the number of degrees C increase) but the root and inboard section can ice up very quickly. It is the assymetric shedding of rotor ice that causes most problems due to the high levels of vibration this can cause.

A colleague of mine went to a helicopter icing convention in London recently and it highlighted how difficult icing is to find when you want it (as Malabo posted) - the only problem is that when you do get caught out it can be very quick and leave you with few options; I know of 2 crews who have been unable to maintain altitude in a Sea King due to icing above mountainous terrain, both of whom were saved by breaking cloud below before they got to the terra firma.

[skadi]

The rotor tips are the last things to ice up because of kinetic heating (IIRC it is the square root of the airspeed that gives the number of degrees C increase) but the root and inboard section can ice up very quickly. It is the assymetric shedding of rotor ice that causes most problems due to the high levels of vibration this can cause.

Another thing is, that the inner area of the rotorblades, where the blades first building up ice, is essential in the case of autorotation. Especially for S/E H/C, after an Enginefailure, you may be unable to build up enough RRPM for a sucsessful landing.

[MightyGem]

I'm sure Mighty Gem will have the exact figures to hand
Unfortunately not. It's been a long time! But, your figures seem about right as far as I can remember. There were also some temperature/time limits as well IIRC, down around minus 8 or 10. The Lynx had heated mats around the intake and hot bleed air into the intakes as well, but forget about any type of blade heating.

The most ice I ever had was about 5mm of rime after 10 minutes in some stratus, but I've been in cloud at 0/-1 and not picked up any.