H2O to Flight

[ScubaRich]

How come a professional pilot who has been scuba diving for over ten years didn't know this???

I AGREE!

 

[sabbath999]

I am an Airline Pilot that would like to do some diving on my 24 hour layovers. What is the time limit for water to wings? The Cabin Altitude is 8500 feet and the duration of the flight is 6 hours. One (maybe two) dive to, probably, no greater than 60 feet.

I googled it and thought I could find the info very easily. All I found was one link at scuba-doc .

thanks,

Scusea

Snorkeling can be great fun too... and you don't have to worry about either getting bent.

 

[Matt S.]

Generally, the computer "no fly" time is just a timer. Read the instructions of your computer. It will generally state that the "no fly" symbol will be present on the display for 12 or 18 hours after a dive, or some variation on that theme. It's not doing any fancy calculations, it's just a timer.

My Suunto was like that. After a 5 minute pool dive, it gave me a no-fly time of 24 hrs, I think.

My current computer, an Uwatec, seems to do some kind of calculation, because I have seen it give no-fly times as short as 4 hours. (I still allow at least 12 or 24, depending on my dive activity.)

 

[sam1]

If you run through the numbers, it is a bit surprising that the required SI actually ends up being less the deeper you go if you stay to the NDL.

For example:
Two different dives to the NDL, one at 50' and one at 110'.

For the 50' dive, you get 100 minutes of bottom time and come up as an L diver. You need slightly over 20 hours before ascending to 8000'.

For the 110' dive, you only get 20 minutes of bottom time and come up as a G diver. You need only 12 hours before ascending to 8000'.

I'm no expert but I have been doing a fair bit of reading recently about decompression modeling and playing around with a model that nearly replicates the NDLs in PADI's RDP. NOAA's tables are reformatted versions of the U.S. Navy's tables. Pressure groups are based on the nitrogen loading of a particular compartment that controlled the dive or, in most cases (in the interest of conservatism), a compartment slower than the compartment that controlled the dive. The U.S. Navy tables use the 120-minute compartment. (An innovation of PADI's RDP is the use of the 60-minute compartment, which is more appropriate for recreational diving.) What tstalcup observed (shorter time to fly for deeper dives [to the NDL limit]) is because the nitrogen loading on the 120-minute compartment (used for the lettered pressure groups) decreases with deeper dives to the NDL limit. This relationship is not true of (most of) the other compartments and is, I think, the reason that the 120-minute compartment was chosen for the basis of the pressure groups.

 

[vladimir]

Generally, the computer "no fly" time is just a timer. Read the instructions of your computer. It will generally state that the "no fly" symbol will be present on the display for 12 or 18 hours after a dive, or some variation on that theme. It's not doing any fancy calculations, it's just a timer.

The Suunto D9 takes the greater of 12 hours and desaturation time, so it will look like just a timer unless you've accumulated a significant amount of nitrogen. If desaturation time is less than 70 minutes no "do not fly time" will be displayed and in gauge mode or permanent error mode 48 hours will be counted down.

 

[Scusea]

All,

Great inputs.....thank you.

Just a little note to the "naysayers": One cannot know something if they don't find out first. I had been told by Scuba Shops the 12 and 18 hour limit was the limit - I told them I was an Airline Pilot. I did not want to stop there so I asked here. You know only what you use. Diving while on a layover comes up very rarely. Usually when I dive I am on vacation OR I have a layover (Navy) well over 24 hours. This is the first occasion I have a 24 hour layover AND somewhere that has really good diving. I began this quest because someone told me the 24 hour rule had been reduced - a rule I always used.

Thank you for the input on CAPA - we don't go by their rules, never heard of them. Thank you for the Chamber Rules - a Chamber typically takes you way way above 8,500ft.

To my knowledge there has never been a FAR that says anything on Scuba. I cannot find one on the FAA web site. I did find the article written by AME Doctors Melchor and Antunano (thank you also for the link). This article is not a FAR - but makes sense and is logical - all I need.

I think I would be fine if I dove using the 12/18 rule. Yet, though very very remote, if my plane did suffer a Rapid Decompression (RD) I MIGHT suffer DCS and I would still need my facilities much more than a passenger would.

SO:

I will continue to use 24 hours as my rule if I work a flight.

Again, thank you for all the inputs.

Scusea

 

[knotical]

Scusea,

You mention Navy. I don’t know about them, but for the Air Force, AFI11-202 at http://www.af.mil/shared/media/epubs/AFI11-202V3.pdf says:

9.8.3. Aircrew members will not fly:
9.8.3.1. Within 24 hours of compressed gas diving

So sticking with your existing 24 hour rule seems appropriate.

There’s probably an equivalent Navy reg.

I suggest adding another caveat: Be free of DCI symptoms.