Breakdown in the Bush: The crash of Airlines PNG flight 1600
On the 13th of October 2011, a de Havilland Canada DHC-8 on descent toward the coastal town of Madang in Papua New Guinea suffered a simultaneous and catastrophic failure of both engines. Without power and falling fast, the pilots had just minutes to find a place to land on a remote and mountainous coastline, leaving them with few good options. At the last moment, they attempted to put the twin turboprop down on the bank of the wild Guabe River, but they hit hard and fast; the plane broke up and a fire engulfed the cabin. In the end, only four people managed to escape, including all three crew and a single passenger, while 28 others perished in the flames.
Despite all appearances, however, investigators soon found themselves delving not into some kind of esoteric mechanical failure, but into the actions of the crew. In fact, startled by an overspeed warning, the captain had wrenched the power levers through a stop and into a position that should only have been accessed while on the ground. With multiple safety systems overridden, the propellers spun out of control until the engines failed. Now faced with a serious emergency, the pilots missed opportunities to stabilize the situation and assess their options, instead rushing into a forced landing for which they were unprepared. But were the pilots really the problem? In the end, investigators would conclude that they were not — plenty of others had made the same mistake in the past, but this time, a failure of governance left their plane without a key safety system that would have prevented the crash.
In the Pacific island nation of Papua New Guinea, known for its far-flung communities isolated between tracts of impenetrable rainforest and precipitous mountains, air travel is the only reliable means to get from one place to another. This reality has encouraged the growth of numerous small, scrappy air operations, ranging from quasi-legal, ad-hoc charter arrangements to proper airlines with larger aircraft and structured schedules. Besides flag carrier Air Niugini, one of the largest domestic airlines is PNG Air, formerly known as Airlines PNG. The rebranding was part of a 2015 effort to promote tourism in Papua New Guinea, but it also helped distance the airline from its checkered past: in fact, between 1987 and 2011, the airline suffered seven fatal crashes, making it one of the most dangerous airlines in a country with an already poor aviation safety record. The most significant, and deadliest, of these accidents was also its last — a sign that perhaps lessons were eventually learned. But as the following story will illustrate, it took nothing less than Papua New Guinea’s worst ever air disaster in order to get there.
On the afternoon of the 13th of October 2011, 28 passengers and 3 crew arrived at Lae Nadzab Airport, located some 33 kilometers outside Lae, Papua New Guinea’s second largest city, for a short scheduled flight to the town of Madang on the island’s northern coast. Most of the passengers were local students and parents headed to a graduation ceremony at the mission-affiliated Divine World University in Madang, but the pilots were not locals at all: 64-year-old Captain Bill Spencer was from Australia, while his 40-year-old First Officer, Campbell Wagstaff, held dual citizenship in Australia and New Zealand. Their presence reflected a lingering colonial legacy, as many of the most important jobs in Papua New Guinea have historically been held by Australians, and it continues to be common practice for PNG airlines to hire Australians with prior experience, rather than training locals from scratch.
The plane they would be flying was a de Havilland Canada DHC-8, universally known as the “Dash 8,” a 37-passenger twin-engine turboprop designed for short, regional flights. Although most DHC-8s were built under the Bombardier brand, this particular aircraft, registered as P2-MCJ, was built in 1988, before Bombardier purchased the original manufacturer. By 2011, the aircraft was 23 years old and was starting to show its age. Captain Spencer and First Officer Wagstaff were probably displeased to discover that several systems had been placarded inoperative, including the yaw damper, a device which automatically moves the rudder to keep the plane flying straight. This failure would force them to make constant rudder inputs to avoid going off course, and it also meant that the autopilot could not be used, so they would have to fly manually all the way to Madang.
At 16:47 local time, P2-MCJ departed Lae, operating Airlines PNG flight 1600 to Madang, a short journey which was expected to take 30 minutes. The flight climbed to its cruising altitude and proceeded northwest, out of the fertile Markham Valley and over the rugged Finisterre Range, a chain of mountains stretching as high as 13,500 feet (4,100 m) along the country’s northern coast. In a testament to Papua New Guinea’s inherent contradictions, the plane passed over the peaks in a matter of minutes, easily crossing a range so remote that its highest mountain was not known to have been climbed until 2014.
After crossing the Finisterre Range, only a short distance across a bay remained before reaching Madang, necessitating a steep descent for a straight-in approach to runway 07. To make matters worse, the bay was choked with scattered clouds at various levels, and they needed to get underneath them in order to see the airport. Flying manually, Captain Spencer pulled the power back and pitched over into a descent, accelerating downward between the clouds.
As the plane descended, it began to pick up speed, accelerating steadily toward the maximum allowable velocity. At the same time, its rate of descent varied between 3,500 and 4,200 feet per minute, much faster than the 2,000-foot-per-minute rate specified for the steepest permissible descent profile, according to standard operating procedures. Focused on getting under the clouds, Spencer didn’t notice that he was flying too fast — until their airspeed reached the maximum operating speed of 250 knots, triggering the overspeed clacker.
Startled by the warning, Spencer instinctively reached over and slammed the power levers back to flight idle in an attempt to reduce their speed. But as soon as he did so, the aircraft was rocked by a massive bang, followed by a deafening whine and heavy vibrations. Smoke suddenly began to pour into the cockpit. “What have we done?” Spencer exclaimed, struggling to make himself heard over the tremendous noise. First Officer Wagstaff replied that both propellers were overspeeding, but Spencer couldn’t hear him. “What have we done?” he repeated. “What have we done!?”
Explaining what he had in fact done requires some background information about the DHC-8’s Pratt & Whitney PW-121 turboprop engines and Hamilton Sundstrand 14SF-7 propellers.
A turboprop engine works by using a turbine to spin a propeller, which forces air backward, generating thrust. The principle behind a propeller blade is actually very similar to that of a wing turned on its side. By angling a propeller blade into the airstream, increasing its angle of attack, the blade actually generates lift, albeit in a forward rather than upward direction, propelling the aircraft through the air.
When the aircraft is stationary with the propeller turning, the relative wind on the blades comes from the side. However, as the speed of the aircraft increases, this relative wind increasingly comes from the front. Therefore, as speed increases, the angle of attack of the blades would decrease, reducing efficiency — which is why all modern propellers come with variable blade pitch. By adjusting the pitch of the blades, as shown above, the optimum angle of attack can be maintained regardless of airspeed.
The blade pitch is measured in terms of the angle of the blade’s chord line relative to its plane of rotation. Blades aligned parallel to the plane of rotation are at zero degrees, and blades perpendicular to the plane of rotation are at 90 degrees. Neither of these positions allow the blade to generate thrust — that requires an angle somewhere in the middle — but each has its own purposes. A blade angle close to zero degrees is useful while on the ground, because the minimal thrust provided by such a configuration is ideal for moving the plane at low speeds across the airport surface. Blade angles below zero degrees can even provide reverse thrust to help slow the plane on landing. Conversely, if an engine fails in flight, it’s important to change the blade angle to 90 degrees, so that the blade edges face into the oncoming air, reducing drag and making the plane easier to control. This is called “feathering” the propeller.
The other important aspect of propeller operation is the rotation speed, measured in rotations per minute, or RPM. Most propellers operate most efficiently within a narrow speed band; for the propellers fitted to the DHC-8–100, this range was 900 to 1,200 RPM. During flight, the pilots can use the condition lever, adjacent to the power levers, to select an RPM within this range, and the propeller control unit, or PCU, will automatically adjust the blade pitch to achieve and maintain this RPM. In fact, blade pitch and propeller speed have an inverse relationship: if the blade pitch is higher, more torque is required to turn the propeller; so assuming torque doesn’t change, the propeller will spin slower, and vice versa. In case of a failure of the PCU, an independent overspeed governor also prevents the propeller speed from exceeding 1,200 RPM by automatically increasing blade pitch until the speed drops back below this value. (A more detailed discussion of overspeed governors can be found in my 2020 article on Pakistan International Airlines flight 661.)
In normal flight, the pilots control engine thrust by selecting a propeller RPM appropriate for the phase of flight, and then increasing or decreasing the engine torque output using the power levers. Increasing torque causes the propeller RPM to rise, so the PCU kicks in, preventing an increase in RPM by increasing the blade pitch. This increases the angle of attack of the blades, resulting in more thrust.
However, when the plane is on the ground and the blade pitch is low, very little torque is actually needed. Therefore, changing the speed of the airplane across the ground is more efficiently accomplished by adjusting blade pitch directly. In order to allow this possibility, the DHC-8 and other turboprop aircraft are designed so that the power levers have two primary “ranges:” a flight (or governing) range where moving the power lever adjusts engine torque, and below that, a ground (or beta) range, where moving the power lever adjusts blade pitch. Using the ground (beta) range of the power lever also bypasses the PCU speed governor and the overspeed governor, so that these systems do not attempt to fight the pilot’s blade pitch inputs. This was acceptable on the DHC-8 because without the additional energy provided by the oncoming airflow, it was actually not possible to achieve a propeller RPM above 1,200 while the plane was on the ground, providing inherent overspeed protection.
On the other hand, this feature also means that if the power lever were moved into the ground (beta) range in flight, there would be nothing to prevent the propeller from overspeeding. Furthermore, in such a case, a propeller overspeed event would be virtually inevitable, due to certain aerodynamic principles.
If you think about it, the only difference between a propeller and a windmill is where the energy to spin it comes from. On a plane, a turbine turns a propeller, causing the blades to “catch” air and force it backward, which propels the plane forward. Conversely, a windmill is stationary, but moving air “catches” the blades, causing the windmill to spin, which in turn drives a generator. Now recall that a lot of torque is required in order to spin a propeller with a high blade angle, but little torque is required to spin the propeller if it has a low blade angle. In normal operation, torque on the propeller comes from the turbine. However, if the speed of the oncoming airflow is greater than the speed of the airflow behind the propeller (that is, the thrust), then the airflow will apply torque to the propeller, just like a windmill. Therefore, if the blade angle is near or below zero degrees (too low to generate appreciable thrust) and the speed of the airplane is high, the torque from the airflow becomes predominant over the torque from the turbine, causing the propeller to accelerate out of control.
This tendency means that moving the power lever into the ground (beta) range in flight is extremely dangerous. In order to prevent this from occurring, turboprop aircraft were required, beginning in the 1980s and 1990s, to have some mechanism which would ensure that the pilot could not accidentally move the power levers into the ground (beta) range while in flight. Generally, manufacturers complied with this requirement by introducing an extra step which would allow movement of the power levers into the ground (beta) range only if the pilot first accomplishes a separate, intentional action. On the DHC-8, accessing the ground (beta) range required that the pilot lift a pair of “triggers” on the underside of the power levers. Actuating these triggers would remove the “flight idle gate,” a physical stop which prevented the power levers from moving below flight idle, the lowest position in the flight (governing) range. Only then could the power levers move into the ground (beta) range.
To provide further assurance, a safety system was included to monitor whether the actual pitch of the propeller blades corresponded to the power lever position. If a propeller’s blade pitch was in the ground (beta) range but that engine’s power lever was in the flight (governing) range, the so-called “beta backup” system would kick in, automatically increasing blade pitch back out of the ground range. However, for obvious reasons, this system would not activate if the pilot put the power levers into the ground (beta) range during flight, because in that case there would be no discrepancy between blade pitch and power lever position.
With all of this in mind, we can now see exactly what happened in those critical seconds on board Airlines PNG flight 1600. As Captain Spencer reached for the power levers, he grabbed them with sufficient vigor to inadvertently raise the triggers, removing the flight idle gate. Still expecting to hit the flight idle gate, he moved the power levers backward with enough force to send them straight through the now-removed gate and into the ground (beta) range. The overspeed governor was disconnected, the propeller blade pitch dropped below safe levels, and the propeller speed rapidly increased beyond the upper limit of 1,200 RPM. Within three seconds, the propellers were spinning so fast that the blade tips broke the sound barrier, triggering a series of deafening bangs. The noise was in fact so loud that it was clearly heard by villagers located several kilometers away and 10,000 feet below.
Although First Officer Wagstaff quickly diagnosed the propeller overspeed, neither pilot immediately noticed that the power levers were in the ground (beta) range. And in the meantime, the situation continued to develop faster than they could anticipate, as the overspeeding propellers began to precipitate additional mechanical failures.
The first failure occurred in the right engine within ten seconds of the beginning of the overspeed event. The failure involved a switch, called the beta switch, whose sole purpose is to detect whether the blade pitch is in the ground (beta) range. When the switch closes, it sends a signal to the beta backup system; if the beta backup system simultaneously detects that the power lever is in the flight (governing) range, it sends a command to increase blade pitch. Then, once blade pitch rises out of the ground range, the beta switch opens, and the beta backup system stops operating.
At some point after the start of the overspeed event, someone moved the right power lever back out of the ground (beta) range, causing blade pitch to increase and ending the overspeed event. At that point, the beta switch should have opened, but perhaps due to deformation of the propeller assembly, it remained closed. Therefore, it continued to erroneously signal that the blade pitch was in the ground (beta) range. With the power lever now in the flight range and the beta switch closed, the conditions to activate the beta backup system were fulfilled, so the system kicked in to increase blade pitch. And because the beta switch had permanently failed closed, the beta backup system simply kept increasing the blade pitch all the way until it hit the stop at 90 degrees. In this “feathered” position, the propeller could not generate any thrust, so the right engine was out of commission. Furthermore, it would be impossible for the pilots to unfeather it, because if they tried to do so, the beta backup system would immediately feather it again.
The failure of the left engine, however, was significantly worse. The propeller speed increased toward 2,000 RPM under the influence of the oncoming airflow, until the torque produced by the propeller itself overcame the torque produced by the engine, and the propeller began to spin the turbine, rather than the other way around. This caused the turbine to overspeed as well, resulting in catastrophic damage as centrifugal forces ripped every single blade straight out of the turbine disks. By the time the pilots moved the left power lever out of the ground (beta) range, stopping the overspeed, the damage had already been done, and this engine would never generate power again.
About 40 seconds after the start of the event, with the right propeller feathered and the left propeller speed under control, the appalling racket finally ceased, and the pilots were able to clearly communicate with each other. They quickly concluded that neither engine was generating thrust, and that they would need to make an immediate emergency landing. By this point they were descending through 7,700 feet over the bay about 18 kilometers southeast of Madang Airport, and at their current descent rate, their chances of making the airport seemed doubtful. Instead, Captain Spencer turned the plane around and headed for the narrow coastal plain where the Finisterre range plunges into the Pacific Ocean, hoping to find a spot to ditch the airplane close to shore. At the same time, he ordered First Officer Wagstaff to inform air traffic control of the situation, and Wagstaff spent the next 63 seconds declaring an emergency, advising the controller of their plan to ditch, and relaying their current GPS coordinates.
With the plane descending between 1,500 and 6,000 feet per minute, only three minutes remained until impact. The overspeed warning briefly sounded again as the plane plunged toward the ground, but Captain Spencer was having difficulty maintaining control. No one had feathered the left propeller, which continued to windmill in the breeze, creating considerable drag on the left side. Combined with the inoperative yaw damper, this made the plane quite unstable in yaw, requiring intense concentration to fly. At the same time, however, Spencer needed to find a place to land. At first he instructed Wagstaff to tell the flight attendant that they would ditch at sea, but just eight seconds later, he spotted what looked like a potential landing site on shore, prompting him to change his mind. What he had spotted was the braided flood plain of the Guabe River, which flowed down out of the mountains and across the coastal lowlands in a series of distinct channels separated by wide pans of gravel. The area looked relatively flat, providing a better landing surface than the ocean. At Spencer’s direction, Wagstaff therefore informed ATC that they would be making a forced landing in the riverbed.
At this point, the pilots finally began trying to reconfigure their airplane. First Officer Wagstaff asked if he should shut down the engines, which were still running despite the absence of thrust. Spencer agreed, and Wagstaff hurried through the engine shutdown memory items, cutting fuel flow and feathering the left propeller. This finally removed the excess drag and improved controllability to the point that Spencer was able to rein in their descent to a more reasonable value. He then directed Wagstaff to give ATC their GPS coordinates again, but this was impossible, because electrical power to the GPS, and nearly everything else, was lost when they shut down the engines.
By then there was little time left to make radio calls anyway. Coming in low over the Guabe River, they were seconds away from landing when Spencer realized, to his horror, that what looked like gravel bars from a distance were actually made out of large boulders dragged down out of the mountains during seasonal floods. If he attempted to land on such a surface, the aircraft would break apart. Thinking quickly, he turned to the right and lined up with the riverbank instead, aiming for an area of open grass with a few scattered trees. At that point, there was nothing left to do but hope for a miracle. Both pilots picked up the public address system and simultaneously called out, “Brace, brace, brace!”
Seconds later, at a speed of 114 knots, Airlines PNG flight 1600 touched down beside the Guabe River on its belly with its landing gear retracted. But Captain Spencer had misjudged the conditions: the bank was covered in boulders, too; he just couldn’t see them because they were hidden by tall grass. As soon as the plane touched down, the boulders and trees began to tear it apart, scouring the fuselage and ripping off the left wing and tail. Fuel ejected from the wing tanks immediately ignited, triggering an explosion as the plane skidded through the brush, surrounded by fire. As it began to slow down, the fuselage snapped in two just behind the forward galley, and the cockpit rolled ahead, coming to rest upside down just beyond the main cabin, which ground to a halt upright but completely ablaze.
Although all or almost all of the passengers survived the impact, their chances of escape were severely reduced by the massive fire which almost immediately engulfed the cabin. In the forward section, which was farther from the blaze, the pilots and the flight attendant managed to extract themselves from the inverted cockpit and galley, respectively, leaving together through the break in the fuselage. Farther back, a Malaysian man seated in seat 7B managed to spot a hole in the ceiling above his seat, and despite intense smoke and fire, he hauled himself through it to safety. Although he burned his arms and back in the process, he was able to move away from the plane and meet up with the crew. Unfortunately, of the 29 passengers, he would be the only one to escape. Photographs taken in the immediate aftermath suggested that two other passengers may have made it as far as the right emergency exit, but they too were overcome by the intense flames and did not survive. Desperate to save anyone they could, local villagers attempted to douse the flames by carrying water from the river inside hollow bamboo stems, but the fire was too large, and there was little they could do.
With 28 passengers dead and only four survivors, the crash of Airlines PNG flight 1600 was tied for the worst air disaster in the post-independence history of Papua New Guinea. That made it the biggest test yet for Papua New Guinea’s new homegrown air crash investigation agency, the Accident Investigation Committee, or AIC. Prior to the establishment of the AIC in 2008, plane crashes in Papua New Guinea were investigated by the Australian Transportation Safety Board (ATSB), and although the ATSB still played a major role, the investigation was led by a PNG national. It was not, however, the first time this had happened: the AIC previously investigated the crash of Airlines PNG flight 4864, which crashed during a failed go-around in 2009, killing 13 people. Now they found themselves at the scene of an even bigger accident involving the same airline. So what had gone wrong this time?
By examining the wreckage and interpreting the contents of the black boxes, the AIC determined that the cause of the crash was Captain Spencer’s inadvertent movement of the power levers into the ground range in flight, resulting in a double propeller overspeed. This raised three main questions: first, why did he do this; second, why did the design of the plane allow this to occur; and third, could the pilots have done anything to ensure a more survivable outcome?
The answers to the first question came from interviews with the pilots and experiments on a representative DHC-8 throttle quadrant.
The sequence of events, in their view, began with the flight’s excessive speed during the descent toward Madang. Captain Spencer said that he was focused on getting beneath the clouds and was not aware that their speed was increasing, nor was First Officer Wagstaff. Consequently, the overspeed warning caught them both by surprise, triggering the Captain’s kneejerk attempt to reduce power. Investigators noted that if the yaw damper had been functioning, allowing the use of the autopilot, then this probably would not have occurred. As an example of manual flying, it was certainly less than stellar.
First Officer Wagstaff told investigators that Captain Spencer pulled the power levers back “quite quickly.” By experimenting with the throttle quadrant, the investigators found that if the pilot attempts to grab the power levers too quickly and forcefully, it is conceivable that they might accidentally lift one of the triggers, releasing the flight idle gate. Furthermore, raising only one of the two triggers by 6 millimeters was sufficient to allow both power levers to travel past the flight idle stop and into the ground range. Investigators also noted that a “beta warning horn” should have sounded when the trigger was lifted, but due to an unknown malfunction, it didn’t start going off until four seconds later. By then it was already drowned out by the sound of the propeller overspeed, and it could only be identified on the cockpit voice recording using sound isolation technology. But in any case, Spencer himself stated that even if he had heard the warning horn, he probably wouldn’t have known what it meant.
The fact that the power levers could be inadvertently placed into the ground range while in flight necessarily led investigators to ask why such a thing was even possible. After all, there was no operational reason for such an input, and the consequences were potentially catastrophic unless corrective action was taken within seconds. So why wasn’t there a lock which could prevent the pilot from moving the power lever into the ground range in flight, even if they wanted to? The answer, as it turned out, was that there was — just not on this aircraft.
The problem of turboprop pilots inadvertently selecting the ground range or the reverse range while in flight was identified decades earlier, and after a string of incidents in the 1980s and early 1990s, regulators began requiring that entry into the ground range be possible only by means of a “separate and distinct action,” such as raising the flight idle gate triggers, that would be difficult to accomplish accidentally. However, incidents continued to happen, some of them because pilots on certain aircraft types were deliberately accessing the ground range in flight (see my 2020 article on Luxair flight 9642 for an example), and others due to inadvertent activation of the triggers. As a result, in the late 1990s the US National Transportation Safety Board recommended that more positive lockout systems be required, and in 2000 the Federal Aviation Administration began issuing a series of Airworthiness Directives mandating various lockout systems that would either make it physically impossible to access the ground range in flight, or would prevent such access from having catastrophic consequences. Among the affected aircraft types was the de Havilland Canada DHC-8.
In order to comply with the Airworthiness Directive, Bombardier Aerospace, which by then managed the DHC-8 type certificate, designed a “beta lockout” system which would keep the overspeed protection system engaged if the ground (beta) range was selected in flight. This system would have ensured that the propeller speed was kept in check even if the pilots accidentally accessed the ground range. If the system had been installed on P2-MCJ, then the engines would not have been damaged and the accident would not have occurred.
Unfortunately, P2-MCJ did not have a beta lockout system because the FAA’s Airworthiness Directive only had authority over US operators. Because Canada was responsible for the DHC-8’s type certificate, only an Airworthiness Directive from Transport Canada could compel foreign operators to modify their airplanes. Yet no such directive was ever issued. In fact, in 2006, an incident occurred involving a DHC-8 in Norway, which prompted Norway’s Accident Investigation Board to recommend installation of a similar system, but Bombardier replied that no such system was needed because inadvertent selection of the ground range in flight was “unlikely to occur.” In absolute terms this may have been the case, but the number of past incidents should have made it clear that it wasn’t unlikely enough. Nevertheless, Transport Canada took Bombardier’s side, declining to issue a directive. Although some countries did follow the FAA in mandating the beta lockout system on the DHC-8, Australia wasn’t one of them, and since Papua New Guinea’s aviation authorities faithfully copy whatever Australia does, the system wasn’t made mandatory in that country either. In this respect, the crash was as much a result of failed governance in Canada, Australia, and Papua New Guinea as it was the result of Captain Spencer’s actions.
Finally, investigators noted that the right engine could have recovered and continued to produce thrust had the beta switch not malfunctioned, causing the propeller to feather. Although the cause of the malfunction could not be determined due to extensive fire damage to the right engine, investigators speculated that the failure of the switch in the closed position was precipitated by deformation of the propeller assembly during the overspeed event. However, in October 2013, late in the investigation, an incident occurred involving a DHC-8 in which a propeller unexpectedly feathered on takeoff as the pilots moved the power levers out of the ground range and into the flight range. The incident resulted in the discovery of a systematic maintenance error at a particular company in the United States, which had been reassembling overhauled DHC-8 propeller control units using an incorrect technique. As a result, the switch housings were bent in such a way as to enable their intermittent failure in the closed position, causing the beta backup system to trigger erroneously. A recall of PCUs which had been overhauled at the facility between 2010 and 2013 was immediately issued. Investigators found that the PCU installed on P2-MCJ’s right engine had also been overhauled at this facility prior to 2010, and may have been affected by the assembly error. If present, the incorrect assembly could have contributed to the switch failing closed when subjected to further strain during the propeller overspeed. On the basis of this finding, the recall was extended to all PCUs overhauled at the facility since 2001.
All of this having been said, one major question remained: could the forced landing have been avoided, or at least made less deadly? The answer, as it turned out, was yes, and it was in this area that the AIC most directly criticized the pilots.
Although it would have been possible to avoid catastrophic damage to the engines if the pilots had quickly discovered their mistake and moved the power levers out of the ground range, the AIC’s analysis assumed that they would not manage to do so in any scenario. (This was already a generous assumption given that in past incidents, pilots generally corrected the mistake in time.) The analysis also assumed that the pilots would be unable to unfeather the right propeller, although the engine was otherwise serviceable. With these elements in mind, investigators considered that it would take the pilots one minute to figure out what was going on and apply the dual engine failure procedure. But in the actual event, they did not follow the dual engine failure procedure, or indeed any other emergency procedure, except for the engine shutdown steps shortly before impact.
Investigators found that if, starting one minute after the failure, the pilots had followed the procedures in the dual engine failure checklist, they could have stayed in the air for nine more minutes, versus three more minutes in the actual flight, and they could have glided at least 18 kilometers. This actually put them just barely in range of Madang Airport, although this was not a realistic option because it was hidden behind clouds and storms had been reported near the runway. Nevertheless, by feathering the left propeller to reduce drag and decelerating to the recommended glide speed of 120 knots, the pilots could have bought themselves six more minutes to deal with the failures and select a landing site. But instead, they didn’t feather the left propeller until late in the sequence of events, and they allowed the plane to descend rapidly at a high airspeed, eating through altitude which they could have traversed more slowly.
Investigators also noted that until First Officer Wagstaff shut down the engines, causing a loss of electrical power, it would have been possible to extend the flaps in order to help slow the plane, but nobody did so. Had the flaps been set to 35 degrees, the normal landing position, then it would have been possible to decelerate to 89 knots before touchdown, 25 knots slower than the speed at which they actually landed. This may well have reduced the damage to the airplane and allowed more people to survive.
Additionally, the pilots never extended the landing gear, which would have helped to absorb the impact forces. The landing gear could even have been extended in the absence of electrical power, and if the pilots had followed the emergency checklist for a forced landing, it would have reminded them to do this. In the event, however, it seems that the pilots initially planned to ditch the plane in the ocean, which would normally be done with the gear retracted, and simply failed to adjust their plans when they decided to set the plane down on land instead.
The AIC investigators speculated that the pilots’ failure to follow the proper emergency checklists may have been due to stress. They were facing a catastrophic situation which appeared without warning and was accompanied by loud noises, smoke, and secondary failures. In such a situation, stress can reduce a pilot’s ability to make informed decisions and exercise judgment. That’s why it’s so important that a pilot is able to react instinctively to an emergency, ensuring that the situation is stabilized before trying to make complicated judgment calls. This kind of reaction can only be inculcated through rigorous training, but investigators noted that neither pilot had been trained to react to a propeller overspeed event, nor had they ever practiced a forced landing in the simulator. Although these topics ideally should be covered in training, Airlines PNG’s training program predated its access to flight simulators, which could replicate scenarios too dangerous to be attempted in the actual airplane. As a result, propeller overspeeds and forced landings were not part of the curriculum.
Investigators also noted that in addition to reduced capacity for judgment, another side effect of stress is a compressed sense of time. In fact, both pilots told investigators that the reason they didn’t carry out any emergency checklists was because there was not enough time. This simply wasn’t the case — in fact, the four minutes and 18 seconds between the onset of the failure and the moment of touchdown were sufficient to perform the dual engine failure and forced landing checklists, especially since the dual engine failure checklist, if carried out, would have bought them six more minutes in the air. Furthermore, too much of the time they did have was spent trying to communicate with air traffic control rather than flying the plane. First Officer Wagstaff spent more than a minute on the radio as the plane was going down, and Captain Spencer repeatedly interjected with suggestions, suggesting that he was listening to the conversation as well. This fact, combined with the pilots’ failure to properly configure their aircraft, represented a violation of the old airman’s principle of “aviate, navigate, communicate.” Unfortunately, too much time was spent communicating, and not enough time was spent aviating and navigating.
As a result of the accident, several safety changes were made. Most importantly, Transport Canada finally issued an Airworthiness Directive mandating the installation of the beta lockout system on all DHC-8s, hopefully preventing a similar accident from ever occurring again. Transport Canada also ordered operational tests of the beta warning horns on all DHC-8s, and Papua New Guinea’s Civil Aviation Safety Authority grounded Airlines PNG’s DHC-8 fleet for 10 days. During that time, the airline held briefings in which they urged pilots to take several mitigating actions, such as keeping one’s hand flat when reducing thrust in order to avoid touching the flight idle gate release triggers. After returning the planes to service, the airline immediately adopted the proposed design changes and stepped up inspections. Although details on other reforms within the company are scarce, it is worth noting that Airlines PNG (now PNG Air) has not had another accident since flight 1600.
As of about 2013, all turboprop airliners in service in most of the world are required to have positive lockout systems that should prevent accidents due to inadvertent or deliberate selection of the ground range in flight. Indeed, as of this writing, no more similar accidents have occurred, compared to at least half a dozen in the decades before the modifications were required. This improvement came hand in hand with an apparent decrease in accidents in Papua New Guinea, which seems to be trying to change its reputation for seat-of-the-pants flying as part of its drive to increase tourism. In the 12 years since the crash of Airlines PNG flight 1600, there have been four fatal crashes in Papua New Guinea, compared to nine in the 12 years preceding it. So far, the data suggests that this is a genuine improvement and not a statistical anomaly.
All of that said, most of the lessons which were learned from this accident could have been learned earlier, as a result of previous crashes and close calls over the years. The FAA recognized that more needed to be done to prevent accidents just like this one, but the failure of other aviation authorities to follow suit represented a tragic lack of imagination and initiative. If they had simply copied the FAA, if they had simply mandated the installation of a simple and inexpensive lock, then 28 people would still be alive. Some might dismiss their deaths as the result of poor safety in Papua New Guinea, but that would be doing them a great disservice. They were failed by well-endowed Western governments that should have known better, and if we refuse to acknowledge that reality, then we will have learned nothing after all.
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