Diving then VFR piloting

[cgvmer]

My son just earned his private pilot's license, currently he only flys VFR, and is working on his IFR commercial etc licenses. He is typically flying in the 4500ft or lower altitude, does this change the fly time recommendations that are given since commercial are pressurized to 8500 ft?

 

[theduckguru]

My son just earned his private pilot's license, currently he only flys VFR, and is working on his IFR commercial etc licenses. He is typically flying in the 4500ft or lower altitude, does this change the fly time recommendations that are given since commercial are pressurized to 8500 ft?

FAA Aeronautical Information Manual

Chapter 8 - Medical Facts For Pilots.


d. Decompression Sickness After Scuba Diving.

1. A pilot or passenger who intends to fly after scuba diving should allow the body sufficient time to rid itself of excess nitrogen absorbed during diving. If not, decompression sickness due to evolved gas can occur during exposure to low altitude and create a serious inflight emergency.

2. The recommended waiting time before going to flight altitudes of up to 8,000 feet is at least 12 hours after diving which has not required controlled ascent (nondecompression stop diving), and at least 24 hours after diving which has required controlled ascent (decompression stop diving). The waiting time before going to flight altitudes above 8,000 feet should be at least 24 hours after any SCUBA dive. These recommended altitudes are actual flight altitudes above mean sea level (AMSL) and not pressurized cabin altitudes. This takes into consideration the risk of decompression of the aircraft during flight.

 

[theduckguru]

message repeat

 

[Dr Deco]

The dive/fly rule is written for ascents to 8,000 feet of altitude. If you are at less altitude, you will have extra protection.

A dive/fly scenario is essentially TWO decompressions. All of the variables associated with one depress are repeated [dive to surface then surface to altitude]. These variables are tissue nuclei number, and size, and nitrogen trapped in bubbles that is not dissolved. The latter means it does not offgas in the manner expected by the calculations.

 

[gcbryan]

The dive/fly rule is written for ascents to 8,000 feet of altitude. If you are at less altitude, you will have extra protection.

A dive/fly scenario is essentially TWO decompressions. All of the variables associated with one depress are repeated [dive to surface then surface to altitude]. These variables are tissue nuclei number, and size, and nitrogen trapped in bubbles that is not dissolved. The latter means it does not offgas in the manner expected by the calculations.

So does this mean that the primary reason no fly calculations are not a simple extension of the dive is because of the inherent muscular activity involved by a diver after he/she is out of the water?

 

[Dr Deco]

The activity level of the diver affects the growth of decompression bubbles. The is fairly well agreed upon. This then translates to increased variability in the second depress [the ascent to altitude]. This is less agreed upon - although I firmly hold that it is true.

The testing that is done does not allow adequately for this variable. If I were the director of a large decompression research program, this would be blended into the study. I was never afforded the opportunity to develop these ideas. Alas!

 

[jamesb]

We used to dive to 100 feet and do a computer aided tour for about 45 minutes ending in 20 feet for 10 minutes, and staying well clear of deco time. We would have lunch and fly home a few hours later at 1500 feet in a small plane. We stopped when I noticed my skin was "crawling", as was another diver in the plane. We descended to 500 feet and it went away? I had thought 1500 feet wasn't significant, and it may well not be.

 

[bleeb]

I wouldn't take this as a definitive answer, but NOAA provides some guidelines:
Required Surface Interval Before Ascent to Altitude after Diving
Note that these use NOAA letter groups, which may be different from everyone else's.

This should maybe be interpreted as criteria for passengers. I've heard arguments that the criteria should maybe be somewhat more strict for a Pilot-In-Command, especially if doing more technical flying like turbine or IFR.