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Inadvertent IMC question

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Inadvertent IMC question

Old 29th Nov 2012, 03:19
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Inadvertent IMC question

Chaps - a hypothetical question from a fixed wing PPL.
I am a non instrument rated pilot in a helicopter below MSA in deteriorating conditions, with steep terrain about a half kilometre away which I am travelling towards at about 120 knots, and being over thick bushland, there is no suitable landing site below.
I inadvertently enter IMC that shows no signs of thinning out, and am overloaded to the point that I can't remember the reciprocal heading to turn back onto.
Is best practise to:
*scan the panel to ensure I am straight and level, maintain airspeed and initiate an immediate climb to above MSA, because the translational lift over the disc will give me best climb performance, or,
*slow to as near to a hover as I can while keeping the aircraft straight and level, pull full collective and rise to above MSA
Question is asked in the context of a recent military crash I was reading about.
I had always thought that inadvertent IMC in a helicopter was less dangerous than a fixed wing because you could simply climb vertically to above MSA. However reading how difficult helicopter IMC flight is, and thinking about the possible disorientating effects of a rapid slow to a near hover while IMC - I'm not so sure.
Anyone able to offer any viewpoints?
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Old 29th Nov 2012, 04:24
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You should not be there in the first place. A lot must have gone wrong in your decision making to end up low, IIMC and above terrain that does not allow a safe precautionary landing, while moving towards high terrain.

Once in that predicament, climb at Vy to above MSA then level, get on your radio and call for vectors.
Any slower and you will have less rate of climb and an even more unstable aircraft. Any faster and you're eating up distance more than necessary while lowering your rate of climb.

Chances are though, you won't survive the climb if you're not accustomed to flying on instruments. And by that I mean more than the minimum exposure to flying the dials. The statistics are just not good.
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Old 29th Nov 2012, 04:39
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So is Vy in a helicopter always at significant enough forward speed to have translational airflow over the main rotor disc?
Or can Vy be attained by being stationary and simply pulling full collective pitch to ascend vertically?
i.e. will I always climb faster if the machine is actually moving forward at speed, rather than acsending vertically from a hover?
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Old 29th Nov 2012, 04:42
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As mentioned, you need speed because the stabilisation surfaces don't kick in until a certain minimum IMC speed, which in the Dauphin is 76 knots. For most light helicopters, it's around 45 knots. You certainly shouldn't hover without a visual reference. You would have around 178 seconds to live, according to Australian figures. Inadvertent IMC is much more dangerous in a helicopter.

Also, as mentioned, you shouldn't be there in the first place, although you can occasionally get caught out, as the helicopter creates its own fog sometimes and you won't realise until you turn round. This is why you need to know the MSA before you take off and who to call at that altitude.


PS - VY is best rate of climb, which you get at a certain sweet spot between lift and drag, so you would climb faster at that speed. VX is best angle of climb, which would certainly be vertical if you had the power, but you would be very unwise to do that.

Last edited by paco; 29th Nov 2012 at 04:45.
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Old 29th Nov 2012, 04:46
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Question answered - thanks guys.
Having struggled to keep a Robbie in a stable hover VFR, I can't imagine what rotary wing IFR must be like.
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Old 29th Nov 2012, 04:53
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1/2 kms to a steep terrain, IMC, 120Kts, below MSA, overloaded, non IFR rated! Hypothetical answer is>> Perfect set-up for a FIT! Can't even call it a CFIT because you'd lose control.
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Old 29th Nov 2012, 05:34
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Just to clarify a bit, Tartare (I guess you're asking in reference to the Kiwi Huey thread on the Military forum):

Lots of helicopters, including the Huey, don't have an airspeed indicating system that will read below about 40 kts. You do have attitude indicators, but the hover attitude is probably about 5 deg nose up and a few degrees left skid low, and will vary depending on loading anyway.

The bottom line is that if you tried to hover (or climb in a hover attitude, ie trying to stay over one spot) with no external reference, you would in reality be drifting around all over the place and it would be extremely hard work.

Secondly, and more importantly in this case I think, a heavily laden Huey may well not be able to hover out of ground effect (OGE), so if you tried to slow to the hover in order to attempt a vertical climb, you might well run out of power and end up going down anyway.

It would be great if you could do it, but having practiced trying to hover on instruments under a hood, it's damn near impossible because you don't have any idea of which way you're drifting - you could be doing 40 kt forwards (or backwards or sideways) without knowing much about it.

For those guys, being in formation would have greatly complicated the issue too, as a formation is a lot less manoueverable than a single ship.
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Old 29th Nov 2012, 05:38
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That's exactly what I was asking about AOTW - thank you, clarifies a lot.
Hadn't thought about the OGE issue.
Had also forgotten of course that to hover effectively you need to pick an external reference point ideally in relation to airframe, and not let it move.
Kind of hard if you are in IMC.

Last edited by tartare; 29th Nov 2012 at 05:39.
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Old 29th Nov 2012, 08:47
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Here's my two penneth:

So you're hypothetically a PPL with virtually no instrument experience who's gone too fast into a situation that has just got you scared stupid. I am assuming that it's now too late to take any of the three options that are appropriate when encountering poor weather (slow down, go down, turn round) and that entering IMC is inevitable. I'm also assuming you're in a light single. That fright that you've just received, and the rapid realisation that you're way out of your depth, is going to significantly reduce your brain's processing ability, so my advice would be to keep the recovery actions as generic and as simple as possible.

1. Straight away, concentrate on your attitude indicator. That's the first step in keeping yourself alive. Put the wings level and the dot on the horizon. (Yes, that will probably induce a slight climb, but that's not a major problem at this point.)

2. Pull in power to your max continuous setting. Do this smoothly, remembering to feed in the appropriate pedal to have a chance of controlling the yaw. (IMO any more than max con for a VFR PPL in IMC is likely to cause control problems, and also needs brain capacity to remember the limit!)

3. Concentrate on the attitude indicator, but also check across to your airspeed - it will almost certainly be reducing if the AI dot is still on the horizon, but not too quickly; peg the speed at about 70 kts by putting the AI dot a couple of degrees below the horizon. (70 kts is a reasonable generic min power speed, hence best rate-of-climb speed, and aids stability. It's also easy for a low-hr PPL to remember, instead of using brain capacity trying to remember what Vy means.)

4. Make sure the slip ball is in the middle, and hold that attitude (with a quick check of the speed every now and then) until you are above MSA. When you get there, smoothly reduce power to something suitable for the cruise, remembering to use the appropriate pedal at the same time.

5. Concentrate on the attitude indicator, with occasional checks of speed, height and heading.

6. Put out a MAYDAY call on whichever ATC frequency you have selected - don't distract yourself from the attitude indicator by changing radio frequencies, otherwise you'll lose it! (There's a good reason, if ever you need one, for always having a suitable ATC frequency selected!)

7. Whatever happens subsequently, concentrate on the attitude indicator (see a theme here?) with occasional quick checks of speed, height and heading.

Even better, use those three options from para 1 before you get anywhere near Inadvertent IMC!

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Old 29th Nov 2012, 09:09
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Tartare: The picture you portray (taken from the NZAF accident) is a 'rotarians' nightmare and several of us have lost friends in similar circumstances.

Some general points of airmanship relating to such conditions: One of first things to address is a reduction in airspeed the moment you find yourself approaching poor vis when in the proximity of terrain - this buys you time (not much) but time nonetheless. If you are in a formation (or even flying in company) this must be broken, as reduced vis + terrain + formed aircraft, do not mix. The flight would (should) have a break procedure.

Should IMC be entered into inadvertently then climbing away is one potential solution but, as discussed, it is not always possible as the aircraft's performance may be restricted. Moreover, unless trained in the practice of IFR, some pilots quickly become disoriented and which usually leads to disaster within seconds.

So what are some of the 'realities' in circumstances such as these? In reality and unless someone is confident enough to 'climb through' (confident not only in their ability to properly control the craft but also that the craft will be able to reach MSA) they will instinctively attempt to recapture VMC and which usually means one of four things; 1) Pushing on in current conditions while praying for an improvement in the vis, 2) Attempting to back-track (I say attempt because it is in attempting this manoeuvre that many souls have perished), 3) Descending (in the hope of exiting IMC), or 4) A combination of all the aforementioned.

While executing the above responses, many many drivers over the years have caught 'lucky breaks' (including yours truly) but, it is probably the most unpleasant of rotary-wing experiences and - many more have paid the ultimate price for 'finding' (or placing) themselves in such circumstances.

In my own case many moons ago and not too far away from New Zealand, my years of flying in Papua New Guinea brought me closer to heaven gates (or maybe even the other place) than I cared for.

Despite the fact that I had a reputation for 'playing it safe' when it came to weather, in a place like PNG if you only flew when the weather was fair, you simply wouldn't fly. Certainly no meaningful work would get done. As you 'learned' the weather you would develop the parameters within which you could safely work but .. that was very much an individual experience for each driver.

One time we had a newbie driver (ex plank) who inadvertently entered IMC in a 500. He ploughed through till he came out on top (I think at around 21,000 feet .. the MSA in most parts of PNG is usually around 19-20k in anycase).

Somehow (before running out of fuel) he managed to find a hole and eventually landed back at Goroka. He was lucky (as well as a few other things that I won't mention here). I remember the ship's entire strap-pack had to be replaced after his exploit.

May I share what often happens as you get older and gain experience? In a sentence .. you basically learn to steer clear of such scenarios. For me, as the years went by, I simply found myself able to better recognise patterns of weather deterioration and its relation to my environment (mountainous and hilly) and to respect the vice of weather. Low fuel and or fading light would cause me to push back, even further, those 'parameters' within which I had found I was able to safely work. That's the 'experience' bit. The 'getting older' bit (spurred by the loss of friends who had perished in circumstances of poor weather) meant that when a pushy client or demanding ops manager piled on the pressure, you simply dug in your heels with that life-saving word .. no!

I have over the past year asked myself several times whether in the case of AJ Smith, Agusta's new 'synthetic vision' would have given him the ability to 'swerve' the hilltop upon which he met his fate. I don't know. Possibly. Perhaps with reduced speed. Synthetic vision may turn out to be a blessing for cases of inadvertent entrance into IMC or .. it could achieve nothing (or even make things worse) if drivers use it to 'extend' the parameters of VMC.

At the end of the day in every single situation, it comes down to airmanship. Professionalism (if one is flying commercially), common sense (or just good airmanship) if you are flying privately and in both cases .. discipline.

The golden rule in this area is a pretty simple one. If you're flying VFR .. keep it that way!
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Old 29th Nov 2012, 09:13
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Inadvertent IMC question
Looked like a deliberate question to me.
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Old 29th Nov 2012, 09:17
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minimum IMC speed, which in the Dauphin is 76 knots.
To be pedantic the min IMC speed is 40kts with other limits as table below:-

IMC flight
The approved IMC envelope is shown at Figure 1
At least one lane of each autopilot channel must be operative.

Minimum airspeed 40 knots (IAS Hold engaged)
Minimum airspeed VY (normal operation)
Maximum airspeed VNE.

The only a/c I have flown that you could climb vertically IMC ( if within HOGE ) is the Seaking which had a doppler meter giving groundspeed in any direction up to 40kts. I only every used it once to climb IMC and that was in the Cairngorms (Scotland) where I had to do an IMC climb from amongst the mountains on a SAR callout. The idea was to fly at min IMC speed commensurate with keeping the doppler meter as near zero as possible, accelerating once past MSA.

I am sure that anybody who tried to hover IMC with no doppler meter would soon meet their maker!

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Old 29th Nov 2012, 09:21
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Telling people it's possible to fly on instruments after Inadvertent IMC on a forum is just plain wrong.

You will not be able to do it. Do not get yourself in that position in the first place. Learn how not to get yourself in that position.

Treat the clouds like rocks as some definitely have rocks inside them. See Sav's post.

Always stay halfway between the cloud base and the ground. When the ground gets too close make sure you can land on it.

In the above scenario as you cannot hover you are now flying a fixed wing.

Would you place yourself in this situation in a fixed wing?

Remember the object of the exercise when getting in the aircraft is the successful completion of the flight, not suck it and see.

The best method is to start with where you want to end up and work backwards to where you are now.

You never want to feel like this guy.

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Old 29th Nov 2012, 09:27
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Where I used to work we had a student who went IIMC for 15 minutes in a Hughes 300 without even an AI to help. Just basic instruments and a turn and slip indicator.

The scenario goes something like this:-

The student was out on a pre PPL x-country navigation exercise who, when caught out by deterioratiing weather put a call out to Christchurch information (NZ) for assistance. Due to his location the radio conversation had to be relayed through a fixed wing aircraft. Somehow, CHCH thought he was an IFR equipped fixed wing aircraft and cleared him to climb to 7000' (ish can't remember the exact figures) The dutiful student that he was, and unbeknown to the amount of poo he was about to be in, he followed the instruction and begun a climb into the cloud.

Shortly after this he tuned up the second com set in the aircraft to our base radio and called in to let us know what was going on?! The very short reply was that he should remain only in contact with information and focus his efforts on flying the aircraft safely. We also didn't want to panic him though there were a number of very ashen faced instructors diving for computers to call up spidertracks. Now, we all new the equipment fitout of the aircraft and also knew that his chances were pretty slim on making it home. We watched the trace climbing up to 6750' ish and breathed a collective sigh of relief everytime we received a new ping. The next ping showed that he was descending and were later told that he was starting to get paniky as he climbed through 7000' and hadn't regained VMC. His next call to control was requesting a descent as not VMC and he was cleared back down to 2000' further descent was to be at his own discretion as he would then be out of radar coverage.

He eventually popped back out of the clouds at 1800' about 15 NM from base and made his way back without further incident. It's my belief that what kept him alive was that equalled to his presence of mind in working out that if he kept the compass pointing the same heading he'd be ok and if he maintained airspeed and power he must have a constant attitude, he also didn't know just how much of the brown he was in and therefore didn't panic.

We all thought that we were watching a dead man on the tracks that day, I am incredibly glad that he isn't and survived to relay his tale. I have told a large number of people about that day and indeed have had friends and collegues get in touch with him and ask questions.

I'm just about to complete my SECIR and would not want to be in a similar situation even with the limited experience that I have, I'm very glad that the trainee in question made it home safely that day. I also tell my students to stay away from clouds as aeroplanes and mountains hide in them.


Last edited by Evil Twin; 29th Nov 2012 at 09:32.
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Old 29th Nov 2012, 09:30
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RVDT: A better graphic illustration I couldn't imagine!

It should be in every pilot's crew room above the words "Dont let weather do this to you".

Well done.
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Old 29th Nov 2012, 09:31
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Fareastdriver - legitimate question - honest.
To others, thanks for your insights - very interesting.
I grew up in NZ and in a former career as a journalist, flew with many NZ helicopter pilots (Alan Bond, Bill Black etc) in dodgy conditions like this.
I was also a fixed wing PPL at the time, so the human factors of rotary wing flight in near IMC is a topic of interest.
I flew with Bondy a few months b4 he died; we hover taxied down the Mt Hutt road in foul conditions, and I was astonished at the airmanship.
Insight from places like PNG is also very interesting - big mountains and rapidly changing weather conditions.
Gentlemen, thanks for sharing your knowledge.
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Old 29th Nov 2012, 10:00
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Your hypothesis is based on the fact that you have an AI in the first place!

They cost a bit more than 2p I think.
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Old 29th Nov 2012, 10:16
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In PNG hardly any of the singles were fitted with an AI.

If inadvertently entering IMC it was down to using the standby compass (for the most basic attitude awareness) and the turn and slip indicator.

Not fun.
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Old 29th Nov 2012, 11:41
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I once got into IMC inadvertely, although I am IFR rated I was flying a non IFR helicopter, I got into low strats clouds 8/8, about 5 min after take off I lost visual references right after a crossed a hill so I imediately concentraded on my attitude indicator (only thing I had), since I had flown that route few times before I knew the MSA, I climbed 200 ft to clear the hill safely on the way back, did a 180 turn, flew the magenta line on the GPS back to the take off site once i got there started decending... and got out, and the pax next to me had no clue on what had just happened..

It felt pretty disconforting getting into IMC without actually planning on doing it specially in a non IFR aircraft, it felt like my mind wasnt ready for it, it was pretty weird.

Last edited by Soave_Pilot; 29th Nov 2012 at 11:41.
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Old 29th Nov 2012, 12:54
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Bare minimums would be to keep the scan of the instruments going, not to fix on only one of them.
If you don't have an AI, the only thing that works is to keep the compass or DG (if you have) pointing in the same direction at the same time as the speed and altimeter should be "glued" on the respective values. (unless of course you need to get to MSA)

I had a not so pleasant experience doing a long ferry over water (lucky enough). I flew through a front I was not briefed about by the Met-office, that came up beyond PNR, and nowhere to land....! I had my IF rating, the helicopter had an AI, DG and an old GPS. I went back to what my instrument instructor told me "pitch, bank, power" (altimeter for pitch, DG for bank and airspeed for power) and kept the scan going until a popped back out again after about 10 minutes in the shit.. (I had radio comms with destination, and knew the weather was good there, and no terrain between, so I fortunately didn't have to climb to get to MSA) By far the longest 10 minutes of my career to date!

As said above, the best is to avoid IIMC altoghter
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