Ever since watching UNDER PRESSURE - Diving Deeper with Human Factors, I've been deeply inspired. I started binge-watching the TV show Mayday (Air Crash Investigation) and taking notes, trying to incorporate aviation concepts into my dive instruction. For example, when teaching buoyancy control, I use the aviation terms Pitch, Yaw, and Roll to define the axes of movement, which makes it much easier to explain what Trim means. I also draw on the analogy of a captain calculating passenger and cargo weight before takeoff — checking whether the load is within limits and where the center of gravity sits — to encourage students not only to calculate how much weight they need, but also to think about where they place it. If your fins are heavy (like Force Fins), and you put all your weights on a weight belt, you'll naturally end up Pitch-Up underwater, floating like a seahorse — head light, feet heavy, generating enormous drag and swimming very inefficiently.
Because aviation accidents involve so many lives, they always trigger multi-national, government-level investigations. Add to that the evidence from black boxes, radar data, and eyewitness accounts, and post-accident analysis tends to be far more thorough and accessible than in diving. So while air crashes are complex events, their rich and varied case studies can, to a meaningful degree, be applied analogously to diving. This approach is worth exploring in depth. For instance, when someone asks me about freediving vs. scuba diving, I can almost always find an aviation parallel: freediving is more like flying a fighter jet — it demands a higher level of physical fitness and leans heavily on anatomy, physiology, and psychology — while scuba diving is more like piloting a commercial airliner, requiring mastery of complex systems and an understanding of mechanical principles and fluid dynamics.
You might ask: are students who have already learned freediving easy to teach when they move on to scuba? I'd say a student who has completed freediving training is like a military pilot transitioning to civilian aviation — they already have a solid physical and psychological foundation. Most of them will sail through the recreational diving curriculum, because passing a freediving course means they already have a baseline in water confidence, snorkeling skills, duck diving, mask clearing, swimming, equalization, line work, and dive buddy awareness. However, that doesn't necessarily mean they'll be able to handle the procedures of technical diving or CCR, or the complex hand-eye coordination and emergency response skills those require. In other words, they might cope fine at the propeller-plane stage of flight school, but not necessarily make it through the full commercial airliner training program.
Let me continue with some video examples that will make it clearer why I use aviation to teach diving:
- 最長距離的滑翔 | 老高與小茉 https://www.youtube.com/watch?v=iUhj8s83w3M
- 瘋狂機長 詹姆士｜跟著老高學空難..越洋航空236 真相解析！ https://www.youtube.com/watch?v=wUybOX4s3r0
Both of these YouTube videos feature aviation YouTuber 老高 discussing air accident cases, with an expert (大佬) stepping in to correct the errors based on professional knowledge. These two videos are also highly instructive, not least as a warning that popular online storytellers — no matter how engaging — aren't necessarily accurate. If you want to learn about diving, watching videos by divers who happen to be influencers can be a decent starting point, but those videos are often riddled with errors. You're always better off seeking answers from a qualified instructor. This particular episode covers the Air Transat Flight 236 accident (also featured in Season 1 of Mayday on National Geographic). I'll leave you to watch it yourself rather than retell the story here.
Photo by Randy Fath on Unsplash
The expert (大佬) carefully walked through several concepts that 老高 had misunderstood:
1. Crossfeed
When the fuel levels in the left and right wing tanks diverge too much, the system triggers a "Fuel Imbalance" warning. Per standard operating procedure (SOP), you must first confirm the imbalance isn't caused by a fuel leak before performing a "crossfeed" — transferring fuel between tanks to restore balance and keep the aircraft flying level. This isn't something you need to worry about with single-tank diving, but once you move into twin-tank configurations, a very similar concept applies. A twin back-mount setup is somewhat like having both wing tanks open with the manifold valve connecting them — both tanks feeding simultaneously. In practice, with back-mount doubles, crossfeed is the default: both cylinders feed through the manifold automatically, and you only isolate them if one side develops a problem. Sidemount diving, on the other hand, offers no automatic crossfeed — you must manually switch between breathing from the left or right cylinder to keep the pressure in both cylinders as equal as possible, maintaining body balance and preventing a Roll to one side. My personal practice is to set my Shearwater dive computer to sidemount mode; once transmitters are installed on both first stage regulators, the computer alerts me when the pressure differential between the two cylinders reaches a set number of bar, reminding me to switch sides and achieve "Fuel Balance."
2. How Do You Know If There's a Fuel Leak?
There are actually many ways to check for a fuel leak — for example, carefully logging the fuel readings at each waypoint and comparing them against your original flight plan will quickly reveal whether consumption is running significantly higher than expected. The same concept exists in diving. Why do we measure our SAC (Surface Air Consumption) rate? Why do we make a dive plan? One key reason is that if your air consumption is running much faster than anticipated, you need situational awareness — you need to recognize that something is off and decide whether to end the dive early or turn back.
In cave diving, when completing the Full Cave course's complex navigation requirement, the final test involves completing a Circuit (a loop route). On the first dive, you mark your position on the main line with a REM slate when you reach your turn pressure, then head back. On the second dive, you enter from the opposite direction. If you encounter the REM marker from the first dive before reaching your own turn pressure, you can continue forward and complete the circuit. This mechanism allows you to determine — based on air consumption — whether to turn back or press on, especially if equipment issues or other factors are causing higher-than-expected gas consumption.
In diving, we often say "expect the unexpected" — a concept taught in risk management courses. Think carefully about what that really means: if you don't know what to expect, how will you even notice when something unexpected happens, let alone respond in time? If you know your SAC rate, if you've made a dive plan so you have a rough idea of your remaining pressure at each waypoint, and if you check your pressure gauge regularly underwater, then when your pressure drops faster than anticipated, you'll actually be in a position to respond before it's too late.
3. Why Aircraft Descend
How high an aircraft can fly — its so-called Service Ceiling — is determined by many factors, just as maximum depth in diving is. In the Air Transat Flight 236 accident, the reason the pilots descended was not what 老高 assumed ("because air density is higher at lower altitudes, providing greater buoyancy and easier aircraft control"). The real reason was that the engines had flamed out, making it impossible to maintain altitude; the crew had to descend to an altitude determined by the aircraft's weight.
Testing how deeply a student understands scuba diving often comes down to asking questions like "How deep can you dive?" or "Why is the depth limit for a given certification level set at xx metres?" For instance, it's common to hear Instagram-friendly divers say "You take the nitrox course to dive deeper" — which reveals a fundamental misunderstanding of MOD (Maximum Operating Depth) and NDL (No-Decompression Limit) parameters. In other words, asking students to explain the reasoning behind key parameters — demanding quantitative understanding, not just qualitative awareness — is a reliable way to gauge how well they actually grasp diving concepts. This is the focus of the oral assessments I give students who have completed their coursework online: for example, asking why an Open Water Diver (PADI/SSI cert) certification carries the depth limit it does. If a student doesn't know the number, or gives the wrong reason, they're doing exactly what 老高 did — using the common-sense guesswork of someone who has never flown a plane to arrive at an incorrect conclusion.
4. Bending Relief
Engines mounted under the wings serve a structural purpose beyond propulsion: their weight counteracts the upward lift force on the wings, preventing them from bending upward and potentially snapping — this is known as Bending Relief. A similar principle applies when teaching beginner scuba divers: as you consume the air in your scuba tank / cylinder, the tank gradually becomes more buoyant, and the bottom of the tank starts to float upward. You need to use tank bands or additional weights to provide "Bending Relief" and keep the tank from riding up. This effect is even more pronounced with back-mount doubles — if the tanks aren't properly weighted and secured, achieving good Trim becomes very difficult.
4. Scuba Logistics Matter
One final concept: equipment isn't just about looking cool. How easy is it to service? How readily available are spare parts? Does it use proprietary sizes or non-standard components? Given how equipment-dependent scuba diving is, logistics are critically important — far more than many beginners realize. It's like the story the expert shared: a flight was going smoothly until the crew was suddenly recalled by the airline because a required component had been found missing from the aircraft on the tarmac — a potential hazard that could have caused a fuel line to detach. Many beginner scuba divers only care about buying gear that looks good, about getting the "top-spec" setup, but because they've never serviced a regulator with their own hands, they rarely think about equipment choices from a maintenance and logistics perspective. It usually takes a real equipment failure for them to truly appreciate the importance of regular servicing at a reputable dive shop.
The above are some personal reflections from my recent teaching experience. If you found this useful, please share it.
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