LOW ALTITUDE Flying after diving

[kelemvor]

I do it regularly myself, and I know what I have decided is safe for me, but I am not going to assume that what I believe is what everyone believes, because there simply isn't any research to support it.

What would a proper study cost? Maybe it is something that could be crowdfunded?

 

[Trace Wilson]

While I am not a pilot, this seems to make the most sense of any.

How can anyone guarantee that weather, traffic, or Air Traffic Control won't require a climb to high altitude?

Second, I fail to see the issue; NE Florida has great ocean diving within an hour or two.

And if you fly to WBP, does that total trip of checking out the plane, filing a flight plan, checking the weather, landing, securing, fueling post checks, and getting a car not take just as much time as the drive?

I hear you on that, but it is more in my control that you would think (@Altamira and any other pilots or ATC members, keep me honest here).

As a private pilot flying VFR (in good weather) and not on a flight plan, ATC has truly no authority over my flight. In fact, I'm not even required by regs to talk to them at all if I can remain outside certain busy airspaces like Miami or Orlando. Flight plans are not a requirement unless you are flying IFR (think flying in bad weather where you can't see what's around you). From talking to other pilots in our Pilots Association and others at various fly-ins, I'd hazard to say that 90%+ of private flights in good weather are not on any sort of flight plan.

The FAA regs also grant me, the Pilot in Command (PIC), the authority to break ANY regulation if required to maintain the safety of the flight or passengers. I would absolutely have to explain my deviation to the FAA afterward, but if the safety of the flight is in question, my decision as PIC is law at that instant. As an absolute last resort, I can declare an Emergency, at which point ATC's basic responsibility is to move heaven, earth to provide me with whatever I need to safely land the plane, including moving every plane they control out of my way and clearing me to land at any airfield I can reach. Again, I will probably have to talk to the FAA afterward (and maybe the military if I land on a base), but the option is there. Note, these are not actions I would ever plan to take, but more just a background of what's allowable to a private flight.

I can, and do, participate voluntarily in 'VFR Flight Following'. In this, ATC will know who I am and assign me a transponder code, but again, they have no authority over me. This is a service they provide, workload permitting, to enhance flight safety where they provide notifications of traffic they see around me, but they have no authority to command me to change course or altitude.

ATC really only has control over flights on IFR flight plans (I'm truly not sure about VFR flight plans because I've never flown under one). When you participate in an IFR flight plan, then ATC then has the responsibility to maintain separation between you and all other aircraft. So, ATC does have the authority to command you on an IFR flight to change course & altitude. The reality is, if I am flying VFR without a flight plan, ATC's responsibility is to get all the IFR traffic out of my way. Again, never having used a VFR flight plan, I ASSUME ATC also has control over them, so they would also get them out of my way as well.

Now, the reality is most private pilots (myself included hopefully) try our best to safe and courteous. Many of us routinely participate in VFR flight following, and when asked by ATC to change our route, we will if able. But again, even under flight following, they can ask me to deviate, but they cannot command it. So, in this instance, if they asked my to climb for some reason, I would simply reply 'unable' and we would find an alternate way of resolving the reason for the climb request.

One other thing I can think of that could require deviation would be a TFR (Temporary Flight Restriction), where the FAA closes small sections of airspace for various reasons (air shows, Presidential visits, etc.). However, these do not pop up instantaneously either. They must be filed, and are listed in NOTAMs (Notice to Airmen). Part of the pre-fight process is to review NOTAMs before takeoff, so TFRs shouldn't be a surprise. And again, avoidance can be handled laterally, not necessarily vertically.

So, the only thing really not under my control is the weather. While it does change somewhat quickly at times, especially in the FL summer, it's not instantaneous. Thunderstorms don't form directly overhead in a matter of minutes, it takes a couple of hours in general. Additionally, they are visible from 20-50 miles away, which provides plenty of time to deviate around them. As a final option, say facing a line of thunderstorms across the sky, I can always land at any public airport and wait for the storm to pass, which usually takes an hour or two. In an absolute worst case, assuming the storm settles in, then I can always rent a car to get home in time for work.

Part of the initial flight planning is to look at the weather forecasts for both going and returning. For long trips, extended forecasts tend be unreliable, but the forecast on Thur. for the upcoming weekend is fairly reliable. If the forecast is calling for bad weather on the return day, then I plan the trip for another weekend. Being located in NE FL and a pilot, I have the luxury of not needing to book airlines etc to get to the keys. If I plan for a particular weekend and the weather doesn't cooperate, then I just reset for the following weekend. Most hotels also allow a 24 hr cancellation. I'm not sure about dive boats, but I would assume they would allow that as well.

For the trip to West Palm Beach, you are correct. While all the pre-flight stuff for the return trip (checking weather, readying the plane, etc.) needs to be done, I would be doing it during the SI after my last dive. Actual travel time, including flight home and drive from the airport to the house would probably save me a total of one hour, so yeah, in that instance it's pretty much a wash. However, where I'm most interested would be a trip to the keys, say Marathon. In that instance the travel time is reduced from 15 hrs round trip to about 5 hrs up the east coast, or 5.5 hrs if weather forces me up the west coast. For a weekend trip, that's a significant difference.

On the diving in NE FL, I'd love to hear of any sites you are aware of that are within OW limits. Everyone I've talked to here says that I'd need to go 20-30 mi offshore to get out of the murk here, and that all the dives are 110-130 ft, which I'm not trained for yet. Additionally, they all say that the dives are really not spectacular, and not something that would bring them back time after time, especially compared to the diving in SE FL. But, if there are sights you know of that would be worth the trip, please pass them along!!

 

[atdotde]

The whole "flying after diving" situation is indeed very mysterious. What is clear is that the current recommendations are not simply based on the well known decompression models extrapolated to ambient pressures in planes (as that would lead to much shorter no fly times at the order of at most a few hours).

You will need to invoke other explanations. One could be that DCS symptoms can appear several hours after the dive. At that point, being in a plane (independent of the question if it was flying that caused those symptoms or if they would have occurred anyway) would not be the ideal circumstances for the treatment of such symptoms.

On the other hand, the standard procedure for what happens when you show DCS symptoms at sea is airlifting with a helicopter. So at least that kind of flying cannot be too bad. But I don't know how your private plane compares to helicopters with regard to altitude.

 

[Trace Wilson]

The whole "flying after diving" situation is indeed very mysterious. What is clear is that the current recommendations are not simply based on the well known decompression models extrapolated to ambient pressures in planes (as that would lead to much shorter no fly times at the order of at most a few hours).

You will need to invoke other explanations. One could be that DCS symptoms can appear several hours after the dive. At that point, being in a plane (independent of the question if it was flying that caused those symptoms or if they would have occurred anyway) would not be the ideal circumstances for the treatment of such symptoms.

On the other hand, the standard procedure for what happens when you show DCS symptoms at sea is airlifting with a helicopter. So at least that kind of flying cannot be too bad. But I don't know how your private plane compares to helicopters with regard to altitude.

@atdotde

Regulations require that I be at 1000 ft over 'densely populated' areas, and 500 ft over 'sparsely populated areas. In this instance, I have the option of flying a short distance offshore up either coast, so I could legally stay as low as 500 ft. My 'plan' would be to be over land, and maintain 1500 ft., which is a standard VFR altitude for west-to-east travel.

 

[flyboy08]

@atdotde

Regulations require that I be at 1000 ft over 'densely populated' areas, and 500 ft over 'sparsely populated areas. In this instance, I have the option of flying a short distance offshore up either coast, so I could legally stay as low as 500 ft. My 'plan' would be to be over land, and maintain 1500 ft., which is a standard VFR altitude for west-to-east travel.

Watch out for the tethered weather balloons in southern Florida

 

[boulderjohn]

What would a proper study cost? Maybe it is something that could be crowdfunded?

It depends upon the study's purpose. The cost could be enormous, and it could be very hard to design to obtain the desired results. Consider driving to altitude and try to count the number of variables that would have to be controlled.

I found a recent study to be very frustrating because a slight change in its design could have produced more valuable results. DAN America's recommends a 12 or 18 minute surface interval before flying. DAN Europe recommends 24 hours. DAN Europe recently did a test on this using Doppler bubble imaging. They tested the divers immediately after a series of dives (IIRC, it was after a liveaboard trip), and then tested them again 24 hours later to see if the 24 hour period was sufficient. When they tested the divers, they were all in great shape, indicating that the 24 hour wait was sufficient. With a slightly different design, they could have found out if it was necessary. As it is, they had no way of knowing when they became OK. It is conceivable that it was after only 6 hours, the length of time it takes the PADI dive tables to wash out. If they had the capacity to test them after 24 hours, they certainly must have had the capacity to test them earlier.

Using similar technology, there are other ideas to test. For example....

• Compare a diver who stayed at the elevation of a dive for a 2-hour surface interval with a diver who drove at a reasonable speed to a 2,000 foot elevation gain over 2 hours. In theory, the diver who took the drive should be safe to ascend that amount even with a quick ascent on a plane. If the diver drove for those 2 hours with a gradual decrease in the PPN2 being inhaled, that diver should be in better shape than the diver who stayed at the same altitude because of the increased off-gassing. If so, the diver who drove to altitude should have had a more efficient surface interval and should be in better shape for another ascent than the diver who stayed at the orignal altitude.
• What about decompression stops during driving? Let's say you are staying in Kona, Hawai'i and want to visit the volcano on the other side at some point after diving. It is greater than a 2,000 foot ascent. If you look at the route, you will see that you will make a safe ascent in elevation, drive at that elevation for a long time, make another ascent, drive at that new elevation for a while, make another safe ascent, etc. How does that compare to make a series of decompression stops during a dive?
• What is the effect of breathing oxygen during a surface interval? Astronauts breathe pure oxygen to eliminate N2 before takeoff and before space walks. I once saw a document that supposedly showed the impact on the NOAA ascent to altitude tables, and it was dramatic. I know divers who breathe oxygen before driving to altitude. I have not found anything official on that, though. It should be easy to test this in a recompression chamber.

 

[Altamira]

I hear you on that, but it is more in my control that you would think (@Altamira and any other pilots or ATC members, keep me honest here).

@Trace Wilson. In the interest of saving space, I did not include most of your post in my response, and am addressing two comments you made about factors that could cause you to deviate from your planned flight altitude. You stated that there were only two things not under your control that could cause you to deviate from your planned altitude: Weather and ATC/Temporary Restricted Areas. I do not know how long you have been flying, what your experience might be, or what airplane you are flying, but I can think of a biggie that perhaps you have not considered. Let's say you are cruising along at 1000 ft above ground or water, and you suddenly have an aircraft malfunction, or worse yet an emergency. What are you going to do? Are you going to stay at 1000 ft, or are you going to climb to a higher altitude to give you additional separation from the ground, giving you as big of a safety margin from hitting the ground/water as possible while trying to sort out your emergency, giving you additional glide distance should your engine(s) quit, and having a better chance of ATC finding you and giving assistance. Having spent most of my military career flying at high speed in very low altitude environments, over land and water, and having had more than a few low altitude emergencies, I can assure you my first reaction was to rapidly increase separation from the thing that will surely kill me: Hitting the ground/water. You have probably heard the venerable saying the three most useless things to a pilot are the sky above you, the runway behind you, and the fuel you left in the refueling truck.

 

[Trace Wilson]

@Trace Wilson. In the interest of saving space, I did not include most of your post in my response, and am addressing two comments you made about factors that could cause you to deviate from your planned flight altitude. You stated that there were only two things not under your control that could cause you to deviate from your planned altitude: Weather and ATC/Temporary Restricted Areas. I do not know how long you have been flying, what your experience might be, or what airplane you are flying, but I can think of a biggie that perhaps you have not considered. Let's say you are cruising along at 1000 ft above ground or water, and you suddenly have an aircraft malfunction, or worse yet an emergency. What are you going to do? Are you going to stay at 1000 ft, or are you going to climb to a higher altitude to give you additional separation from the ground, giving you as big of a safety margin from hitting the ground/water as possible while trying to sort out your emergency, giving you additional glide distance should your engine(s) quit, and having a better chance of ATC finding you and giving assistance. Having spent most of my military career flying at high speed in very low altitude environments, over land and water, and having had more than a few low altitude emergencies, I can assure you my first reaction was to rapidly increase separation from the thing that will surely kill me: Hitting the ground/water. You have probably heard the venerable saying the three most useless things to a pilot are the sky above you, the runway behind you, and the fuel you left in the refueling truck.

Touche!

 

[gr8jab]

Could you just plan and execute your diving as if they were altitude dives at 2000 ft, then just jump in the plane and go? Or am I way off base, since you had not acclimated to 2000 ft before and between the dives?

 

[boulderjohn]

Could you just plan and execute your diving as if they were altitude dives at 2000 ft, then just jump in the plane and go? Or am I way off base, since you had not acclimated to 2000 ft before and between the dives?

The issue is that ascending to higher altitude moves your body from one ambient pressure to a lesser one, as if you are ascending during a dive. The problem is that we do not have the ability to predict your specific ascent the way dive tables or a computer define the specifics of your dive. Look at the US Navy ascent to altitude table posted earlier in this thread. It attempts to do something specific using the US Navy dive tables. ee how complicated they are.

In contrast, the flying after diving guidelines cover ALL diving. That means they must be super conservative for some divers, and not so conservative for others.

What you are suggesting in your post is that if you dive a little more conservatively, will that work? What you are suggesting is the equivalent of diving to the E pressure group in the Navy tables rather than the F pressure group and thinking that will make you safe with the flying after diving guidelines. Maybe it will. Maybe it won't. The DAN flying after diving guidelines don't differentiate. The US Navy tables do.