Tec45 Sidemount Course – F4 Phantom (45m) Check-Out Dive
By Andy Davis, PADI and ANDI technical and sidemount course instructor
In June 2012, I ran a PADI Sidemount Course in combination with the TecRec Tec40/Tec45 program, based out of Subic Bay, Philippines. These are photos from the graduation dive – conducted on the Vietnam-era F4 Phantom supersonic fighter-bomber.
The F4 Phantom wreck is located several kilometers outside of Subic Bay and lies at a depth of 45m/147ft. Visibility is typically excellent and the current is typically mild-moderate. More details on the wreck are listed here: Subic Bay Dive Sites
The training started with a 3-day Sidemount course, followed by the 3-day/4-dive Tec40 and Tec45 courses. These introduce the skills and procedures necessary to use sidemount configuration, followed by advanced nitrox and accelerated decompression procedures training.
For details of sidemount diving and configuration, please check out my Sidemount Course Notes.
It was acceptable weather for the dive, cloudy, occasional showers with a slight onshore breeze… the Philippines monsoon season was just coming into effect at this time of the year. My student, Elias, and I took a mid-morning speedboat trip for several kilometers beyond the mouth of Subic Bay, heading south in the direction of Manila. At a site pre-designated by GPS, the boat crew dropped the shot-line overboard (as it turns out, with great accuracy) and we began to gear up.
A number of configurations and philosophies are covered on the sidemount course, developing the student’s ability to configure themselves safely and effectively for technical sidemount dives with 3-4 cylinders.
On this course, the student was using a Razor 2 sidemount harness/BCD, with Apeks sidemount regulators. Courses have also been taught using the Hollis SMS100 and OMS Tessaract/Profile systems.
Having donned our sidemount harnesses/BCDs, masks and fins, we entered the water and were handed out sidemount cylinders. These are easy to fit whilst in the water, with little difficulty in a 1/2m swell and slight current. Had the surface conditions been any more demanding, we could have fitted the cylinders on the boat.
Following a brief surface check, we began the descent. Conducting Bubble Checks and S-Drills at 5m, we enjoyed descending in the clear blue water… feeling free and unencumbered. The water was very clear and shafts of dappled sun-light cut the blue around us as we dropped deeper. After a few minutes of controlled descent, the distinctive silhouette of the F4 Phantom began to slowly resolve against the blueness beneath us. It’s always a nice relief to see your objective on descent – because mistakes in site location have been known to happen…even with the benefit of GPS location.
Sidemount training, once completed, permits the diver to conduct all subsequent training in that configuration. Many divers are now realizing the advantages of sidemount configuration. It is becoming a very popular starting point for technical diving training, in lieu of the traditional ‘back-mounted’ doubles.
Upon nearing the bottom of our shot-line, it became obvious that the line was located about 12m off to the side of the aircraft. Visibility was sufficient to see the wreck, but we couldn’t guarantee seeing the line from the jet upon return. The solution was to deploy a finger reel and run a guideline direct from the shot-line to the F4.
We reached the wreck, and signaled/agreed to stow our deco tanks and proceeded to explore the wrecked jet. Our bottom time was planned for 25 minutes – plenty of opportunity to explore and poke around the jet. In order to achieve that, we had calculated an additional 20 minutes of decompression obligation, leading to a planned dive run-time of 49 minutes.
The Tec40 course is the entry-level technical diving course offered by PADI. It equips the diver to conduct limited decompression (10 minutes non-accelerated), using one deco tank (nitrox to 50%, deco planned as per back-gas), to a maximum depth of 40m.
The course is heavily focused upon the development of ‘core’ skills – buoyancy, trim, control, awareness, along with intense equipment familiarity and refining the level of precision applied to dive planning and conduct.
Combined with pre-training, in the form of the Tec Sidemount Course – there is ample time for a relatively experienced recreational diver to master the equipment, as well as the myriad of new skills, drills and procedures needed to safely exceed recreational diving limitations.
Our guideline was tied on at the mid-section of the place, so we decided to venture towards the nose area. The wreck was covered in small schooling fish, with a couple of whooping Groupers hanging around the jet intakes. At this depth, there was no discernible current and lots of ambient light. Perhaps a little narcosis was in play, but both myself and my student were enjoying the dive and big grins were the flavor of the day.
The F4 Phantom is a supersonic (Mach 2.23) two-seat, twin-engine interceptor/fighter/bomber, that entered U.S Navy service in 1960, later being adopted also by the U.S. Marines and Air Force, along with several other national air forces, including the RAF (I remember the RAF Phantoms being serving out of Cyprus in the late 80′s). The aircraft served with distinction during the Vietnam War. It was last used operationally during the 1991 Gulf War in an anti-radar/air-defense suppression role, before retiring in 1996.
The aircraft was very high technology for it’s era, fitted with an advanced doppler radar, impressive payload options and having an airframe mostly composed of titanium. The good news for future generations of technical divers is that the titanium structure should be around for a long time!
Subic Bay was a major re-fit and maintenance location for the U.S.Navy during the Vietnam conflict, so many hundreds of F4s would have visited here. We examined the engine cowling and intakes…and it quickly became clear that the J79 engines were not present. The conclusion is that this was an ‘expired’ airframe that was stripped and dumped at sea from a carrier.
The course demands a consistently high level of core diving skills, ingrained equipment familiarity and the focus necessary to develop and carry out a more complicated multi-stop decompression schedule.
Having inspected the mid-section and engine intakes, we made our way to the cockpit. The canopy was removed, as were the two ejection seats – further confirming the theory that this was a stripped down airframe. As we were using sidemount kit, it was an easy task to partially remove/unclip the side-slung cylinders and ease ourselves into the cockpit for a cheeky photograph. Not many people get to sit in the cockpit of a veteran supersonic fighter… even less get to do so 150ft underwater!
By this point, we were approaching 20 minutes of bottom-time, so it was time to conduct a final poke around the nose section, before heading back to collect our staged deco tanks and ascending. Precision is everything on a technical dive – and we had to make sure we were back on our shot-line and prepared for ascent without over-staying – as this would have a near-exponential impact lengthening our decompression schedule.
The next step would be the Tec50 course, which further develops the diver’s ability to safely plan and conduct technical dives to a maximum depth of 50m, using nitrox to 1oo% for unlimited decompression with multiple deco tanks/mixes.
Re-acquiring our deco cylinders was an easy process, as we’d practiced this skill many times during the preceding Tec40 and Tec45 training dives. We quickly noted our contents tags, confirming names and mixes, before re-attached the deco tanks to our rigs. The finger spool was a good judgement call, as the seconds were now counting down and we couldn’t see the shot-line from the wreck. If we’d had to search, there was a good chance that we’d have blown our dive plan.
Winding in the spool led us directly to the ascent line, and with a quick ‘OK’ we began our lengthy and controlled return to the surface. Our dive plan called for an ascent rate of 10m per minute, so after 4 minutes of ascent and a 1 minute ‘deep stop’ at 28m, we arrived at our first formal decompression stop depth of 12m. We completed 2 minutes of deco there, before ascending again to 9m for a further 6 minute stop.
Our next scheduled stop was at 6m for 4 minutes. We were decompressing with 100% O2 so, upon arrival at stop depth we conducted a NOTOX gas switching procedure, moving onto the rich deco gas to reduce the length of decompression. At this depth, pure oxygen is on the borderline of its maximum safe partial pressure. Dropping below that depth threshold (breathing oxygen at a deeper depth than 6m) can induce rapid oxygen toxicity – which causes convulsions and, consequently, drowning. It is at times like this when students realize the profound value of the seemingly endless practice of buoyancy control and awareness conducted on the tech courses.
Having hovered patiently for 4 minutes, we ascended again to our final stop – 3m for 8 minutes. Time always seems to pass slowly when conducting decompression stops, but there was chance for some final practice of the cylinder shut-down procedures and air-sharing. As our timing devices flickered to 49 minutes, right-on-schedule, we began our final slow ascent to the surface. The boat was waiting for us, but the weather had deteriorated during the dive. Luckily, sidemount configuration championed itself again… and the process of disconnect and passing up our cylinders made boarding the speedboat a swift and painless process.
With wide smiles, we enjoyed our fast ride back to the dive center – and even a torrential deluge of proportions only experienced in the topics during monsoon couldn’t dampen our spirits (although the rain did sting somewhat). Congratulations to another member of the technical diving community – an excellent performance by Elias and a really fun 12 days of training conducted!
For more details about Technical Diving and Sidemount courses, please feel free to contact me.
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