What QNH would you use if ditching?
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What QNH would you use if ditching?
Was having a discussion with one of our Captains today and he asked me this question.
Night, engines failed, no radio altimeter obviously, what QNH would you set?
After thinking for a second, I figured of course it would be the Current QNH.
He was very convinced that he should set standard.
I don't see how standard would be useful considering you almost never have standard pressure or temperature.
If Current QNH will show you elevation at airdrome when youre on the runway, shouldn't it read 0 above sea?
I'd appreciate input on this.
Also while on this topic, another irrelevant ques, I am trying to remember the little concept from flight school.
When youre at std 1013, and change to QNH which is 1030.
Changing from low to high gives you a lower alt.
LOW - HIGH - LOW
Just making sure this is correct.
Night, engines failed, no radio altimeter obviously, what QNH would you set?
After thinking for a second, I figured of course it would be the Current QNH.
He was very convinced that he should set standard.
I don't see how standard would be useful considering you almost never have standard pressure or temperature.
If Current QNH will show you elevation at airdrome when youre on the runway, shouldn't it read 0 above sea?
I'd appreciate input on this.
Also while on this topic, another irrelevant ques, I am trying to remember the little concept from flight school.
When youre at std 1013, and change to QNH which is 1030.
Changing from low to high gives you a lower alt.
LOW - HIGH - LOW
Just making sure this is correct.
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gcc_
Was having a discussion with one of our Captains today and he asked me this
question.
Night, engines failed, no radio altimeter obviously, what QNH would you set?
Was having a discussion with one of our Captains today and he asked me this
question.
Night, engines failed, no radio altimeter obviously, what QNH would you set?
If over the sea; then when you think you are close to sea level, lights on and use the mark one eye ball, if over land when you switch on the lights and you dont like what you see then turn them off and hope for the best.
Last edited by Above The Clouds; 10th Jun 2012 at 21:41.
Also while on this topic, another irrelevant ques, I am trying to remember the little concept from flight school.
When youre at std 1013, and change to QNH which is 1030.
Changing from low to high gives you a lower alt.
LOW - HIGH - LOW
Just making sure this is correct.
When youre at std 1013, and change to QNH which is 1030.
Changing from low to high gives you a lower alt.
LOW - HIGH - LOW
Just making sure this is correct.
As for ditching I'd definitely set the best QNH I had access to. Either the local QNH of a near by airfield or the area QNH. It won't be perfect but it'll be a lot better than setting 1013 which would be useless. What was your captain's reasoning for setting 1013?
Last edited by AerocatS2A; 10th Jun 2012 at 22:25.
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If it is daytime VFR it doesn't matter. At night it might be nice to have an accurate altimiter setting but with wing landing lights on it would be the same. Ask Sully if he ever looked at the altimeter and his reply would be WHY? Any competent pilot in visual conditions should be able to ditch by eye ball navigation. The altimiter is not required. This may not work for an autopilot monitoring pilot, only for a real pilot.
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I didn't say Sully used his eye balls to decide where to land but how to ditch. What I said was the eye ball in visual conditions is the only way to touch down in the proper attitude and speed. He did it well and we all hope we could have done the same. The altimiter is unnecesary once you have chosen your touch down ditching spot.
Hopefully we all could have done the same thing. We aren't really trained for it but we all should have the skill to do it.
The new autopilot monitor guys with low time won't be able to do it unfortunately. The old guys can.
Hopefully we all could have done the same thing. We aren't really trained for it but we all should have the skill to do it.
The new autopilot monitor guys with low time won't be able to do it unfortunately. The old guys can.
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energy circle
everything I read says he didn't use the ''energy circle"... also, FWIW 4 pilots repeated the scenario in the simulator and turned right away to LGA and all made it.
so I really don't think the energy circle was working...I understand he was in a situation that didn't display this option.
and for the question, use the best one available by radio, or by knowledge of the general pressure situation over the ocean. standard is one way to go without additional knowledge...but if you know you are flying over an area of high pressure...you might want to adjust things
but you would be advised of lowest useable flight levels if pressure was way off.
everything I read says he didn't use the ''energy circle"... also, FWIW 4 pilots repeated the scenario in the simulator and turned right away to LGA and all made it.
so I really don't think the energy circle was working...I understand he was in a situation that didn't display this option.
and for the question, use the best one available by radio, or by knowledge of the general pressure situation over the ocean. standard is one way to go without additional knowledge...but if you know you are flying over an area of high pressure...you might want to adjust things
but you would be advised of lowest useable flight levels if pressure was way off.
Heavens to murgatroyd,
You are landing an airliner with no engine power into the water and you are worried about what QNH to set? I would have thought there would be other things higher on the "to-do" list in this situation.
You are landing an airliner with no engine power into the water and you are worried about what QNH to set? I would have thought there would be other things higher on the "to-do" list in this situation.
I would have thought there would be other things higher on the "to-do" list in this situation.
Stabilised approach criteria come into their own in these situations as an overrun of the designated landing area could be critical. Also, after touchdown, all usages of left and right must be replaced with "port" and "starboard", the F/O should be addressed as "first mate" and the in-charge cabin crew as "bosun".
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If Current QNH will show you elevation at airdrome when youre on the runway, shouldn't it read 0 above sea?
When youre at std 1013, and change to QNH which is 1030.
Changing from low to high gives you a lower alt.
LOW - HIGH - LOW
Just making sure this is correct.
Changing from low to high gives you a lower alt.
LOW - HIGH - LOW
Just making sure this is correct.
Remember of Altimeter errors though
Ditching is a visual maneuver.
Last edited by de facto; 11th Jun 2012 at 09:20.
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Why not just wait until your belly touches the water? When it does, zero your altimeter and you'll be able to read a reasonably accurate QNH (within instrument limitations) from your kollsman window. Especially handy should you have to go missed off your initial ditching attempt for any reason...
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At 200' cross check with your radar altimeter. If they don't agree go-around and reset your altimeters. Do the after takeoff checklist, climb checklist, descent checklist and before landing checklist, and then, and only then, attempt the ditching.
The investigators will be all over you if you continue the approach with the wrong altimeter settings!
Repeat after me - procedure, SOP, procedure, SOP, procedure, SOP... it will save you.
The investigators will be all over you if you continue the approach with the wrong altimeter settings!
Repeat after me - procedure, SOP, procedure, SOP, procedure, SOP... it will save you.
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Agaricus bisporus
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Who cares? Haven't you got better things to be doing? If you really need height info use the rad alt!
Dear me!
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Who cares? Haven't you got better things to be doing? If you really need height info use the rad alt!
Dear me!
Now since we are in the tech forum,are you sure the RAs would work ?
I think honestly for a night ditching it would be best to set up a very shallow glide similar to a 'glassy water' landing. however that maybe difficult to do with no power....but I don't think an accurate altimeter would be of that much help in the scenario you describe