Perils of PNG

The fate of the Twin Otter– impacting a steep, high elevation, jungle clad mountainside in low cloud and rain — conformed to a PNG accident pattern that has cost many lives and aircraft over the years since flying became “the only way to travel” in the island’s mountainous interior. Indeed, it could be said that the aviation environment of Papua New Guinea is amongst the most challenging in the world.

A recently published list entitled, Some PNG Fatal Accidents over the Years, contained more than 150 entries – and the list is by no means exhaustive. In many of the listed cases, the aircraft were flown by highly experienced pilots, with years of PNG flying behind them. One major accident at Kainantu involved a Twin Otter operating an airline scheduled service. The pilot and several of his passengers were killed and some who survived were disabled for life.

Papua New Guinea operations abound in pitfalls for even the most experienced pilots. Airstrips in the interior are for the most part situated amid dense tropical jungle, many of them at high elevations. Some can be reached only by transiting through the gaps in the high, steep-sided mountain ranges, often cloud-enshrouded and subject to heavy rain for much of each day, particularly in the afternoons.

Many of these strips, carved from mountain slopes, are extremely short, with steep overall gradients, necessitating uphill landings and downhill take-offs. To complicate the situation further, most lie on hillsides or ridges in narrow valleys and canyons that allow no second chance during an approach –- once committed, a touchdown of some sort has to be completed, or a crash (often fatal) will be the inevitable result –- simply because the topography does not allow an aircraft to go around.

A typical case some years ago involved a twin-engined aircraft approaching Chimbu in the Wahgi Valley after a cargo flight from Madang. Chimbu’s former grass airstrip on the crown of a hill, (now replaced by a better strip at Kundiawa), was less than 530m long and oriented north-south, with an up-slope of 1 in 25 from south to north. On its western side, the ground rose steeply to mountain ranges, while on the eastern and southern sides, the undulating ground fell away to the Chimbu River. Landings were only possible into the north and all operations were prohibited in downwind conditions. Though the strip’s elevation was 4900ft, the density altitude at the time was 7700ft.

When over the Chimbu threshold, an updraft suddenly lifted the aircraft more than 50 feet. The pilot began a missed approach, and the aircraft was seen to fly along the strip at low level then, still flying slowly, begin a 180o turn to the right. The turn quickly steepened but when almost completed the nose of the aircraft dropped and it crashed on to a down-sloping spur less than 300m north-east of the end of the strip. The pilot, the only occupant, suffered serious injuries and the aircraft was destroyed. The turn, progressively steepened to avoid the intervening spur, had begun at too low an airspeed, with a stall the result. Experienced PNG pilots agreed that a missed approach should not have been attempted. A crash landing on the airstrip was the only alternative.

A rare exception to this general rule was achieved by a Cessna 206 pilot by performing an “instant” stall turn into the ravine beside the mountain strip at Aseki, inland from the Huon Gulf. The pilot “got away” with this extremely risky manoeuvre, averting a collision with a Piper Aztec on the ground, only because the C206, flying into the strip to pick up bags of coffee beans, had no load on board. Other aircraft that attempted similar “go arounds” at Aseki on two later occasions both crashed.

The precipitous jungle clad ranges forming the “spine” of the interior of Papua New Guinea, include mountain peaks rising to almost 15,000 feet, while many of the passes and gaps in the ranges have an elevation of 8000 feet or higher. Density altitude considerations thus become a serious problem. And often to reach remote airstrips it is necessary to fly up narrow valleys below the cloudbase. The problem then becomes one of recognising the right entrance to the valley amongst the mountains. Some of the valleys are “blind”, becoming progressively too narrow for an aircraft to turn and fly out again if the pilot has mistaken the entrance. A catastrophic accident is thus inevitable if the pilot has misidentified the valley entrance.

Because of the elevation and nature of the terrain, instrument flight rules are out of the question for all but high flying aircraft. In any case, PNG’s NDBs are often affected by atmospheric interference. Accurate visual navigation is thus highly critical. A thorough knowledge of the country and its weather is essential, as well as high manipulative skills, and a detailed knowledge of the aircraft’s handling characteristics.

A former RAAF flying instructor tells of an incident during a training exercise in the PNG Highlands in a Hawker Sidderley 748.

“We took off from Madang after lunch, planning to visit Mount Hagen, Minj and Banz along the Waghi Valley, surrounded by mountain ranges of up to 14,000 feet. The airstrip lengths were just adequate for our planned weights at the high density altitude take-offs and landings involved.

”Climbing to 15,000 feet, we headed for Minj, some 100 miles south-west over rugged country. As we passed over the Ramu Valley, heavy cloud was covering the mountain gaps adjacent to the 14,800ft Mount Wilhelm. PNG weather is characterized by massive cloud build-ups over the ranges by early afternoon, but the HS-748 has good altitude capability and I knew that, providing we stayed VMC, we could climb out of trouble.

“With only five minutes to our ETA for Minj, reports told us heavy rain was reducing visibility around Mount Hagen to the north-west and Goroka to the south-east. One report was of lowering visibility in the Waghi Valley. We dropped the landing gear, and lost height in a series of turns to keep clear of stratus and towering cumulus, but the sight of rain clouds drifting across the base of the mountains leading down to the valley made me uneasy. Cloud around Minj was low and black, and we had to circle at 1000 feet above the valley to get a pinpoint. Neither Minj, or nearby Banz, were visible in the rain.

“Once under the main cloud base, we could see dark veils of rain cloud blocking both ends of the Wahgi Valley, so I felt the time had come to get back to Madang – and fast! The cloud break we had descended through had already filled over, and so close to the mountains, it would have been suicidal to climb in IMC. We were relieved to spot a TAA Twin Otter emerging from the rain and heading down the valley for Goroka, and I turned to follow him.

“As we flew past the tiny airstrip of Chimbu on a ridge overlooking the Chimbu River, I made a mental note that as a last resort I would plant the HS-748 squarely on the threshold, and work out how to get out of the place once safely ensconced. Meanwhile the Twin Otter had drawn ahead and was disappearing in the heavy rain.

“This was getting serious, so I hauled into a steep turn back towards the clear air near Chimbu. A few minutes later we were orbiting Chimbu with the awful realisation that this tiny grass strip, balanced precariously on a narrow ridge, was going to be our home for the night. In my mind I could already visualize the waiting military Court Martial. Why had I pressed on regardless into the Wahgi Valley, despite other aircraft reporting the weather closing in?

“By now, I had run out of ideas — like it or not, I had to get the 748 on the ground before the approaching rain cut visibility to zero. I have seldom felt so alone, so I asked the crew for suggestions. The navigator thought it might be worth flying north along the Chimbu River valley to see if the Bundi Gap into the Ramu River plains was open. But on both sides of the Chimbu valley, the mountains disappeared into cloud, and it was a gamble I decided not to take –- there was also the danger of the weather socking in at Chimbu while we were poking our noses up the river gorge. In any case, I was not confident I could recognize the Bundi Gap if I saw it.

“With a deep breath, I announced we were committed to land at Chimbu, and I set the aircraft up for a precautionary approach. But as we straightened up on final, we spotted rays of sunlight slanting against the rising ground a mile or so up the gorge. And where there is sunlight, there must be a hole!

“I opened the throttles, retracted the gear and flaps, and keeping to one side of the gorge to allow for a tight one-eighty, checked out the sunbeams. To our relief, the gap in the cloud seemed just enough for a circling climb — though we would lose out badly if we were forced into steep climbing turns. There was also the possibility of the cloud closing, trapping us in IMC as we circled upwards.

“I decided instead to zoom climb at full power until forced to lower the nose, then resume a spiral climb to keep within the edges of the cloud hole until we were safely on top. Turning back to allow room to manoeuvre, I switched on the water methanol to give the engines full boost and, once in position, went to full take-off power. Feeling the water methanol kick in, I dived towards the scattered sunlight on the mountain side at maximum speed — plus some!

“When the sun glinted on our wings, I looked up at patches of blue sky thousands of feet above, and decided it was a goer. Hauling back, I rocketed that aeroplane as steeply as I dared, keeping a close eye on the rapidly unwinding airspeed.

“An hour later we were safely back at the Smuggler’s Inn at Madang! The whole episode was a memorable experience — in hindsight, I should have turned back when reports indicated bad weather at both ends of the Wahgi Valley and we were still safely on top of cloud.”
The RAAF instructor’s summing up is echoed by a highly experienced PNG civil pilot whose general advice for operations there is “only fly where you can see.”

An instance of an Australian pilot venturing into PNG in a Cessna 182 without an adequate understanding of its environment also speaks for itself, a fatal accident probably being averted only because of the intervention of three experienced PNG pilots.

“A highly experienced PNG pilot’s general advice for operations there is “only fly where you can see.”

One of them, flying to Nipa in the Highlands, overheard the C182 reporting weather problems en route to Koroba, 40 miles north-west of Nipa. Encountering heavy cloud, the C182 pilot had turned back, sighted the strip at Nipa and landed to get his bearings. He then decided to continue to Tari, about 15 miles short of his destination. But hearing a charter aircraft would be landing in a few minutes, decided to wait and ask the best route to Tari.

On landing at Nipa, the charter pilot was amazed to learn the C182 pilot was inexperienced, with almost no knowledge of PNG conditions. After pointing out to him some of its hazards, the charter pilot radioed another aircraft for a report on Tari weather. This was unfavourable, with cloud to 13,000 feet, so he invited the visiting pilot to follow him back to Mendi and spend the night there. The C182 could then follow another Mendi-based aircraft to Koroba the next morning.

But as they were boarding their respective aircraft, the charter pilot had second thoughts about the C182’s load “With the quartering tailwind,” he said later, “I knew I wouldn’t be able to lift more than 225kg from Nipa in my Cessna 206. On checking the C182’s load, I found there was more than 300kg on board, so I’m quite sure it would have crashed. Nipa is 880m long and relatively flat but, surrounded by rising ground, it is deceptive. It would be possible to lift a full load from the strip, but impossible to out-climb the rising ground. So I transferred one passenger and all the luggage from the C182 before leading it back to Mendi.”

At Mendi both aircraft were met by another PNG pilot flying a Cessna 402 who “quickly gained the impression that the C182 pilot’s knowledge and experience were slight, to say the least. He also had no idea of leaning the fuel mixture for altitude, so I instructed him how to arrive at mixture settings for high altitude take-offs.”

After the overnight stop at Mendi, it was arranged for the C402 to accompany the visiting Cessna to Koroba. What followed is related by the C402 pilot:

“Before taking off, I explained the length, slope and nature of the surface at Koroba, (560m long, with one-way operations on a three per cent up-slope), pointing out the need to approach with the utmost caution in a short field landing configuration.

“I told the C182 pilot to take off first and to wait at the Hum Gap, four miles north of Mendi, while I caught up. But after I took off, the Cessna was nowhere to be seen. On making contact on VHF, it was obvious he had become lost. I orbited for 15 minutes, trying to ascertain his position. He finally caught up with me, and we set course for Koroba. En route, I went to great pains to explain the ground features and airfields, making sure he was correlating my information with his map, as he would have to make his way back unaided.

“Weather conditions at Koroba were marginal with low cloud over the strip, so I landed first and gave him detailed advice, describing the type of circuit he should make. I also reiterated the importance of deciding early whether the approach was satisfactory and making a decision whether or not to go around. Despite this, the C182 was very high on final, and the pilot only made a safe landing by reducing power completely and violently pointing the nose down.”

The PNG pilot said later that the visiting pilot “was in grave danger of doing injury to himself. His techniques were rusty and his knowledge of his aircraft’s performance inadequate. His map-reading and navigation were poor, and his coming to PNG placed a burden on all concerned, from Flight Service Officers trying to relate his position to his flight plan, to pilots who had to go out of their way to help him avoid disaster.”

These experiences demonstrate the demands placed upon professional PNG pilots every working day, requiring exceptional standards of aeronautical knowledge, airmanship and manipulative skill. A number of PNG airstrips are more than 7000 feet above sea level, an even larger number less than 600m long, with average slopes of up to 13 per cent. Portions of some are even steeper. Such strips are difficult even for experienced pilots, and density heights approaching 10,000 feet are not uncommon.

A further indication of the level of ability required in Papua-New Guinea is that before being authorised to act in command of commercial flights, pilots are required to complete five return trips over the route and on to the airstrip concerned, two of them as observer or co-pilot and the remainder as pilot-in-command under supervision. They are also then subject to six-monthly checks. The checking and training is supervised by the particular operator’s chief pilot, who in turn holds an authorisation from the PNG Civil Aviation Administration.

“These experiences demonstrate the demands placed upon professional PNG pilots every working day require exceptional standards of aeronautical knowledge, airmanship and manipulative skill.”

Despite the everyday hazards of flying in PNG, and its long history of accidents, countless flights to difficult inland destinations are completed safely under demanding conditions every day. These services are simply taken for granted by those who live in the PNG inland. This in itself is a tribute both to the skill and professionalism of the pilots to whom these trips are “all in a day’s work”, and the safeguards of the checking and training systems in place.

The overall value of aviation to the people of PNG is inestimable, both for providing access and supplies to inaccessible centres of population and isolated villages, and of course for the provision of medical services, particularly in cases of emergency. Without aviation, PNG as a nation would be quite unable to function.

Captions:

PNG 01:
Widespread areas of low cloud and violent tropical storms are among the hazards encountered in everyday PNG flying.

PNG 02:
Operations into Efogi, 3800 feet AMSL on the Kokoda Track, make heavy demands on pilots’ judgements. The one-way strip is only 335m long and has a 9.5% upslope.

PNG 03:
Cloud on the hills surrounding Boana. The rising ground close to the airstrip leaves little room for error during an approach to land.

PNG 04:
Surrounded by cloud-enshrouded mountains, Omkalai, 5500ft up a valley side, is a constant challenge to the skill of PNG pilots for whom such difficult operating conditions are daily demands. This one-way strip is amongst the most steeply sloping in PNG, and pilots are advised “to maintain momentum with power after touching down in order to negotiate the steep slope”.

PNG 05:

Situated between the edge of a ravine and towering peaks is Tarpini, 3000ft AMSL. This picture illustrates the nature of the rugged terrain surrounding this difficult airstrip, and its characteristic cloud cover.

PNG 06:

The variable slope of the Tarpini strip is evident in this picture looking back along the landing path. The maximum gradient is 11.6% and full power has to be applied immediately on landing to reach the parking area at the top of the slope.

PNG 07 and 07A:

Chimbu airstrip in the Wahgi Valley is less than 530m long, with an up-slope of 1 in 25 from south to north.

PNG 08:

Marginal VMC: Heavy cloud over the steep-sided Erave River valley in the Southern Highlands. The photograph was snapped en route to the Erave airstrip

PNG 09:

Low cloud encountered in the Snake River valley between Bulolo and Lae.

PNG 10:

Cloud-enshrouded mountains bordering the Oksapmin Valley between Oksapmin and Telefomin in the Western Highlands.

PNG 11:

Impending doom. This picture was taken from the right hand seat of a Piper Aztec flying up a blind valley near Kokoda en route from Port Moresby to Lae. The pilot, making his first visit to PNG, was unfamiliar with the route and lost his way near Efogi, mistaking the blind valley for the entrance to the Kokoda Gap. Only minutes after this picture was taken, the Aztec crashed on the steep valley side and its four occupants were killed. The camera was found alongside the wreckage.