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Topical Tropical Tips

Topical Tropical Tips

A recent spate of accidents in the treacherous rural conditions of South East Asia has once again thrown the spotlight on operating helicopters in tropical, mountainous terrain.

Recent accidents in SE Asia:

  • 6 July 2012. Papua New Guinea. Bell 206. Crashed into tropical jungle. Three fatal, no survivors. Low cloud and poor visibility reported in media.
  • 21 July 2012. Kuching, Malaysia. EC120. Crashed into river. Three fatal, one survivor. Family reported inclement weather concerns before flight.
  • 22 July 2012. Island of Borneo. Military Bell 212. Crashed into tropical terrain. Twelve fatal, two survivors. Poor weather reported in media.

Military historians tell us that at the end of World War II, 300 aircraft were still missing in Papua New Guineas and the nearby coastal waters. This loss rate is extraordinary and indicates how inexperience, high performance aircraft, minimal training and the stresses of war, when combined, can be deadly.

For those of you inexperienced in flying in Papua and New Guinea, or any other tropical mountainous country for that that matter, it might be useful to hear a few suggestions learned from hard if not bitter experience.

Flying in the tropics is not the same as in the southern latitudes, and the margin for error is considerably less. A helicopter that is docile and forgiving at low density altitudes becomes very critical of coarse handling at very high density altitudes and when it bites, it bites quickly and savagely.

Basically, we will deal with the weather, high altitude, and navigation, separately even if they are all inter-related.

Weather: Limestone or granite filled cloud is a trap for pilots who press on into rapidly changing conditions. PNG is actually littered with wreckage of aircraft all with the same basic configuration – just below the top of the ridge and in plan form, still maintaining their basic shape. Not hard to figure out what happened in every case: in cloud, supposedly at a safe height, see the terrain at the last second, and desperately pull up to try to get over it. The aircraft mushes into the trees parallel to the very steep ridge with little or no indicated airspeed, but a ginormous vertical impact into the slope. It ain’t economical to do any more than get the bodies out, and there isn’t much to salvage any way. Moral (strange to have to say it) never fly into cloud if you are VFR!

Remember that the vertical development of cloud can get you just as much as horizontal movement. It can begin to clear above 5,000’ in the early morning, but by eight o’clock the anabatic wind is quietly moving clouds up the mountains. If you are sitting on the ground, mind in neutral, on a 10,000’ mountain, you may find you have no way down. You mostly have to fly between layers of clouds during the day because the terrain is so high, but never forget the layers are usually slowly climbing. It is a sad thing to be on top of unbroken cloud as far as the eye can see, believe me.

As I’ve preached before, your weather planning is a continuous thing. You must always have an escape route. If you plan to cross a ridge and can see another ridge ten minutes away, you don’t continue unless you can guarantee that the weather won’t close you in during that ten minutes, or the first gap will stay open until you can turn around and get back across if you have to. Don’t be like the missionary Cessna pilot I watched day after day heading off into a narrow gorge upstream with cloud sitting on the top, and faced with a right angle turn into God knows what a mile or so into it. He had faith, alright.

Have a succession of fields or pads picked out (and sadly there aren’t too many), that if you do get stocked in, you can set down for a while and wait for things to improve. Fortunately, it doesn’t take long in the tropics, and you should be going again in ten or twenty minutes – though I’ve spent the odd night in some funny places!

As you can imagine, the weather you can see around you is all-important, and forecasts made by the met man several hundred miles away don’t rate much more than casual interest for local operations. I trust that the level of forecasting has improved since I first started flying in PNG; for a flight from Moresby to Kerema I was assured of 15 knot headwinds. After pushing 25 knots all the way, and landing with bare fuel minimums, I called up the forecaster to let him know of the unforecast conditions. The next day the recorded forecast was upped to 25 knots, but the state of the trees when I got out to the helicopter company prompted me to call again, and he blithely advised me it was actually 50 knots over most of the coast, except one place that had no reported winds – as the anemometer and windsock had blown away!

You have to assess the conditions as far as you see them, but call up your destination and places en route longer flights, and most importantly, talk to other pilots in the area. This is especially so when you are tracking from the coast to the highlands, which could involve passing through several cloud layers while heading towards higher and higher mountains.

Visibility is critical, and can be restricted from morning fog and cloud to absolutely torrential rain. If you are flying slowly, you don’t get the slipstream clearing the windscreen; fly sideways and accept getting wet if you have the doors off. If you do have doors on, be prepared for windscreen fogging. The humidity will always be higher than you are used to. Another phenomenon with tropical weather: occasionally you can see a bright blue in the middle of torrential rain. It isn’t necessarily blue sky a short way through the rain, but just the colour of a particular nasty thunderstorm – as I found out to my horror on a routine flight from Mount Hagen to Goroka. I don’t know what I was thinking, as I just been up to 9,000’ trying to find a way through, then back to 6,000’ (or 1,000’ above the Wahgi Valley). Anyway, there it was: bright blue just ahead so I thought I’ll just punch through. I finally broke out on top of 11,500’ after a max rate climb on a heading I hoped would keep me between the 14,000’ mountains either side.

That’s when I really knew what some of the pilots of those wrecks scattered through the place were thinking in the final minutes of their lives!

Torrential rain also doesn’t do your helicopter any good other than giving it a good wash. Rotor blades can get rapidly eroded, so make sure your blade tape (if fitted) is in good condition. Be alert for any increase in vibration – which means that the tape is starting to rip away or delamination. Get on the ground before the vibration builds up to a point which could damage the aircraft.

Altitude. You hopefully are well aware of the effects of increased altitude on blade efficiency, fuel consumption, engine power, load carrying ability, and so on. Some factors you may never have encountered in temperate climes is the lack of ability of the turbine engine to spool up quickly from a low power setting; the IAS/TAS relationship; or how quickly you can overpitched the main rotor or lose tail rotor effectiveness (LTE).

The IAS/TAS problem merely means at very high altitudes, your true airspeed can be considerably higher than your indicated airspeed. Do some pilot computer calculations even if you don’t believe me. What it means is if you start an approach with 30 knots on the ASI, you are going much faster over the ground, and you can feel it. You could be suckered into thinking you have a tail wind, or you could start an approach much faster than you should, considering everything else is critical. A mate approaching in a Squirrel at a density altitude well over 12,000’ was a tad fast (Why? Probably the IAS/TAS problem.). He reduced collective to the minimum in the final stages of the approach, and then he quickly pulled in a lot of collective coming to the hover. The rotor RPM began dropping as the engine thought about it for a few seconds and then started to wind up. But it was then too late – the Squirrel became a crumpled heap on the ground.

Over pitching is very exciting; I once overpitched three times in a Bell 47 coming up to a hover on Mount Otto, each time thumping firmly down on the pad while my passengers fervently and rapidly crossed themselves. A bit of religion comes in handy in the aviation industry! You should note I made no attempt to move forward until the hover stabilised; so the only damage done was to my pride. Of course you must be aware of those helicopters which are more prone to LTE and carefully think through the approach to ensure you minimise your exposure to that potentially catastrophic loss of control.

At very high density altitudes, you do everything slowly and carefully. Keep your eye firmly on your rotor RPM, it should be at the top of the green before committing to any landing or takeoff, and don’t allow any bleed-off. Make all approaches slow and controlled, with at least 30% torque throughout the approach in the turbine powered machines. The same rule applies to turbo-charged piston engine helicopters.

Navigation: In Australia we are fortunate to have accurate maps and charts which are regularly updated. In PNG, as with most tropical countries, your maps may leave a lot to be desired; the detail may be iffy, the scale might not be suitable for precise navigation, and man-made features may not be represented or could be shown several miles from where they actually are. Now, GPS is God’s gift to pilots, but it may quit when you least want it to (happened to me once 100 miles out to sea tracking between islands –ah, such memories), and it doesn’t give you the optimum track to your destination, which is so much dictated by the weather around you. And worse, it becomes like a drug. You tend to over rely on it so that your basic navigation and upgrading skills get rusty, and worst of all you don’t memorise the terrain. Come the day when you can see only a bit of ground below you through a cloud layer and you can’t recognise it because you’ve been lazy. So, you’re lost. And that can kill you. And GPS doesn’t prevent you turning up the wrong valley or re-entrant; that’s another major killer of the unwary or the inexperienced in PNG, because there is often no room to turn. Use the GPS as it’s supposed to be, as a backup!

Another problem that you normally won’t find in Australia is the physical change in the appearance of the terrain from day to day, because of the vertical aspect of the ground and weather. One day you fly through a valley at 5,000’ with cloud above and below, the same valley next day at 7,000’, again between layers, and then the day after at 10,000’. The terrain is totally different each day, and you won’t see anything that you saw on the other days. It takes a lot of getting used to. It means that you have to use your altimeter as part of your navigation, to relate contours and features on your map.

The technique that works best for me was to draw a rough track on the map, then if I had to divert or meander around and away from it, I had it firmly fixed in my mind as to which side I was off the track. I knew which way to meander back. The 1 in 60 rule doesn’t get much use in PNG! In keeping with the principle of escape routes, I recommended noting down villages or clearings that you can come back to, along with the time you pass them.

Flying in PNG is exhilarating, with spectacular scenery and sights, but it can be very unforgiving. You learn a lot very quickly, and I think are a better pilot for the experience there. If you go there, fly carefully to be safe, talk to the experienced pilots already there and get their advice, and enjoy your adventure!

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