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Beware flying LL over glassy sea

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Beware flying LL over glassy sea

Old 16th Nov 2015, 10:26
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Originally Posted by Herod
A friend of mine used to fly low enough to get wave-lift, which supposedly cut fuel consumption. If my understanding is correct, this means flying at less than half the wingspan above the water, without a rad alt. Luckily, I never flew with him.

Sounds like he was using ground effect.
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Old 16th Nov 2015, 11:04
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Sounds like he was using ground effect.
Though the effect is available, I can't imagine a reason to fly low enough to use it in a P-51 on a fun flight with no need to get somewhere. With a non pilot passenger, he would already be impressed at the speed of the aircraft, so the small ground effect increase would be meaningless. I would also think that no P-51 pilot would be deliberately taking a passenger that close to the water, there is not reason.

As the non pilot seemed to be flying, I can imagine the pilot distracted, providing verbal guidance to the use of controls etc. and "head in" for a crucial period. A non pilot would be ineffective at maintaining altitude over a featureless surface, and the P-51 could develop an awesome descent rate with few cues. I opine that this accident could have had it's fate sealed several hundred feet up.
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Old 16th Nov 2015, 16:21
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This is a worthy discussion of glassy water and losing situational awareness but nobody has yet mentioned Kennedy's loosing everything on his way to Martha's vinyard with two pax on board. He had no instrument rating; conditions over the water were getting dangerous, horizon ref had gone.
Which side is up? how can you tell?

The complete opposite to the amazing viz in your photos of that glassy water surface, promising clarity, no wind, no ripples, no boats....and situational awareness, relying on what you can see (the bottom of the lake) - oops!

and responding to Down West -

Over Scapa Flow, during the war, he describes how his old man was surprised that the other pilot was flying so close to the surface! "he grabbed the stick, only to find it loose - they both thought the other was flying the a/c"

Reminded me of the story about a tutor tandem 2 seat training glider, where the instructor had the evil habit of testing his student's composure by saying "Well, you are flying so well I don't need this any more!" and he would toss his control stick over the side.

Until a savvy student in the front of the Tutor replied "Well, I guess I don't need this any more either!" and tossed HIS stick over the side as well...

Needless to say the student had only tossed over a spare.. remarks by the instructor from the open cockpit could be clearly heard by all the happy spectators on the airfield....

(humble apologies for thread creep....)
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Old 16th Nov 2015, 22:41
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Though also over water, JFK jr.'s accident is a rather different loss of awareness. He should have been trained to recognized that in that environment, not only is the water not usable as a "surface" reference, there simply is none. You are effectively not flying VFR anymore, and must recognize that, and fly with reference to the instruments, even though you are still in VMC. No one would think to attempt to fly 50 feet of the water, at night, using the surface of the water as the reference.

Over glassy water, you are flying in decent if not very nice weather, with the surface in clear sight. But, it is not a suitable reference for establishing altitude within 100 feet. It is not a matter of seeing the bottom through the water, it's the reflection on the water which makes it difficult to judge height.
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Old 17th Nov 2015, 08:57
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In cavok weather, with sea not glassy, but no white caps, at 3000' with no land in sight, blue sky and blue sea can merge in the distance with no horizon.
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Old 17th Nov 2015, 09:30
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I was cruising in a Prentice at about 5,000 ft (I thought) quite soon after sunrise, on route from Rhodes to Cyprus. It was a lovely, cloudless morning, but very hazy, with little visual reference. I was very tired and drowsy, having slept fitfully under the aircraft until getting up at 0400 or so to get going.

After a while, I noticed sparkling flashes, rather like a distant firework display, seemingly above my height. Hmmm, I thought, AAA practice? Nothing on the map and Rhodes briefing room said nothing. I watched this for a while, forgetting to scan, and then, I'm suspect, dozed off for a few moments. (The Prentice rumbled along at 1900 RPM, quite soporific really. No autopilot or wing-leveller, of course, but very stable.)

Then I woke up, either literally or metaphorically, and scanned automatically; Dear God... altimeter....500 ft!.... VSI....descending at about 200 fpm.

The aircraft had been slightly nose-down in a gentle descent for quite a while, and the flashes were the rising sun's reflection, through the haze, off the ripples in the sea's surface near the horizon I couldn't see in the haze, seen in the top of the windshield because of the aircraft's attitude.
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Old 17th Nov 2015, 10:06
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Glad you woke up in the nick of time!

I bet from then on you kept the aircraft trimmed slightly nose up while in cruise.
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Old 17th Nov 2015, 11:19
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a really informative and interesting thread that any flyer should have a good read of whether a newbie or not

i fly with a friends Bulldog over and around Portland and Weymouth but usually we only get flat calms about once day a year

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Old 17th Nov 2015, 12:31
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The very sad BAH S-61N accident off St Mary's might be of interest - low level, calm sea and poor vis, coupled with an unintentional descent.
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Old 17th Nov 2015, 17:10
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Mary M,
The old man told me that story too! Though I think it was in a powered a/c.

When TOM asked the other pilot what he thought about the incident, he replied that he thought they were a 'bit' low, but didn't want to ask a senior officer if he knew what he was doing..... ( Father was an FO at the time)
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Old 18th Nov 2015, 03:21
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I used to fly with a gent (his day job was in the right seat of a HP Herald ex EGMC for British Air Ferries) whose favourite party trick was buzzing around the coast in a C152 at 100' AMSL or thereabouts, waving at the fishing boats.

However, as soon as he established himself straight and level, he'd dial in a bit of nose-up trim, so that a certain amount of forward pressure was needed to stay there. The thinking being that if he momentarily lost attention for any reason, the aircraft would tend to climb away from trouble rather than the opposite.
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Old 23rd Dec 2015, 13:15
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This report shows that even highly experienced and well trained pilots can be a victim of over water CFI"T":

Aviation Investigation Report A13H0002 - Transportation Safety Board of Canada

In particular, sections: 1.17.4, 1.18.7, 1.18.8, 2.3 and 3 are worth a read.
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Old 24th Dec 2015, 02:24
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Agreed Chuck, though I venture a guess that you were doing it in a large flying boat. That would offer a bit more useful altitude for the "1/2 wingspan" often considered ideal for ground effect. And, I expect that the ocean is rarely glassy, so visually determining your altitude was a bit more certain.

In a small flying boat, I have found that I have to have the keel just a few feet up to experience any ground effect, and that's too low for any sane person to fly a landplane over water at cruise speed!

In any case, if the water is or suddenly becomes glassy, determining your altitude visually will suddenly become impossible, and immediate climb is the only safe action.
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Old 24th Dec 2015, 04:45
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Max Conrad said he used this technique in a PA-24 Comanche in setting an eye watering distance record of 12,341.26 km (7,668.50 mi) - Casablanca - Trinidad - El Paso - Los Angeles- non stop of course.

Or it may have been his record flight in a PA-30 Twin Comanche - 12,678.83 km (7,878.26 mi) Cape Town - St Petersburg FL.

It is written about in the biography by Sally Buegeleisen - Into the Wind, The Story of Max Conrad. An interesting read.
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Old 24th Dec 2015, 21:31
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If you are flying in ground effect with a surface rough enough to accurately judge height it will not suddenly turn into complete glassy water so fast you will crash and die before you recognize the surface has changed into complete glassy water, because the very fact you are flying very close to the surface dictates you are being very careful watching your height.
The vital key is to recognize the sudden change to glassy, and begin to climb immediately. The light ripple you're flying over can become glassy in an instant if the gentle breeze ceases. When you fly from the rippled area, to the glassy area, there will suddenly be no way to judge your height, so you'd better be in the climb. Or, if in a seaplane, perform a glassy water landing.

Similar circumstances can occur flying low over snow - one minute there's a pattern, and you can judge your height, the next the pattern is gone, and the surface is featureless, you'd better climb!
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Old 24th Dec 2015, 22:13
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I have deleted my posts because they did not add anything worth while to this discussion.

And more important I would not want someone to get killed because I posted something that was bad advice like I have done here.

My problem is I have lost the ability to articulate what I am trying to say and also the world of aviation has changed and moved forward since I was in it, thankfully I survived in spite of my lack of in depth education and real understanding of what I was doing.

Last edited by Chuck Ellsworth; 25th Dec 2015 at 00:34.
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Old 23rd Jan 2016, 16:47
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Basil, sorry to be so late to the party. But your
Recollect a Hastings captain remarking to his co-pilot how difficult it was to judge height above a glassy sea just before there was a bang and the two inner props were bent. They survived.
reminded me that I was on that squadron at that time. You might be interested in a bit more of the story.

Because of the wing dihedral, the Hastings' two inner engines were, I think, four inches lower than the outers. So four inches was the margin of error - and indeed the two inners did stop, with bent props.

Now, the Hasty-bird did not go well on two (didn't go all that well on three, come to that). But at the time they were North of Cyprus, not far from Kyrenia, and didn't have the fuel to get round the island to Akrotiri. Anyway, they were based at Nicosia. But the problem was, how to get over the mountains along the panhandle. They managed it.... just.

The captain was required to present himself for a no-coffee interview, which was closely followed by hearty congratulations for getting one of HM's valuable Hasty-birds back more or less in one piece.


Last edited by airsound; 23rd Jan 2016 at 17:45. Reason: spelling
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Old 23rd Jan 2016, 22:01
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A glassy water landing I flew, as video'd by my passenger. My height above the surface could not be distinguished, and this was a no flare landing. The stall warning heard was actually after I was on the water, when I raised the nose a bit to assure the desired attitude while slowing.

That was not the right video!

Last edited by 9 lives; 27th Jan 2016 at 16:01.
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Old 27th Jan 2016, 12:15
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There's a bloody large hotel at your 6, and a tea lodge at your 1. BTW, you're in Alberta.
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Old 30th Jan 2016, 19:38
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I thought about this thread when I saw this magnificent photo yesterday on a calendar, while standing in line at a TDCanada Trust bank branch:

A Snowy Owl - definitely in ground effect and gliding over an almost featureless surface.

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