Landing (descent or approach)

At about 1038 hours on Tuesday 7 January 1997, Polynesian Airlines’ DHC-6 (Twin Otter) 5W FAU collided with the western slopes of Mt Vaea, Apia, in conditions of low cloud and heavy rain. The aeroplane was on a scheduled flight from Pago Pago to Fagali’i, and was being flown to Fagali’i by visual reference after having made an instrument approach to Faleolo. The captain and two passengers lost their lives in the accident. The first officer and one passenger survived.

After executing a missed approach at the Grand Canyon Airport, the pilots diverted to the Bullhead City Airport. The pilots reported that minimal icing conditions were encountered with about 1/8 inch of ice accumulating on the aircraft wings. The pilots stated they cycled the deice boots to shed ice. They did not observe ice on the propeller spinners, and they did not activate the engines' 'override' ignition systems, as required by the airplane's flight manual. Use of 'override' ignition was required for flight into visible moisture at or below +5 degrees Celsius (+41 degrees Fahrenheit) to prevent ice ingestion/flameouts. Subsequently, both engines flamed out as the airplane was on about a 3 mile final approach for landing with the landing gear and flaps extended. The aircraft was destroyed during an off-airport landing.

The aircraft departed Exeter at 2237 hrs where the weather was fair with scattered cloud at 1500 feet. After climbing uneventfully through cloud to FL 90 the aircraft cruisedin clear, smooth air. In the cruise the co-pilot noticed that his vertical speed indicator was displaying a slight rate of climb although the aircraft was in level flight but this and a spurious hydraulic warning were the only anomalies. As the aircraft approached East Midlands airport the runway visual range there was below the approach minima and several aircraft were holding awaiting an improvement in the visibility. G-ZAPC descended to 2,500 ft and held in clear air over the Lichfield NDB for about 45 minutes until the fuel state dictated a diversion to Liverpool. On diversion the aircraft was initially cleared direct to the Whitegate NDB and then Wallasey VOR at FL 40. At this level the crew could see ground features in good visibility until they entered cloudas they descended through 3,500 feet whilst being radar vectored for an approach to Liverpool Airport. The cloud was stratiform in character and did not appear to contain precipitation or significant turbulence. At Liverpool airport the cloud base was 6/8at 1,100 feet, the visibility 12 km, the air temperature +1°Cand the surface wind was 060°/8 kt. There is an ILS localiser on Runway 09 but no glidepath transmitter so a LOC DME approach is normally flown. Although the DME antenna is mid-way along the runway, the DMErange is set to read zero at the runway displaced threshold. The pilot flies the localiser in azimuth and adjusts his height according to his pressure altimeter; the 3° glidepath commences at 1,610 feet QNH from 5 nm DME with check heights at 4, 3, 2 and 1 nm DME. On the north side of the runway 329 metres from the threshold there are 4 PAPI (Precision Approach Path Indicator)lights which are set to a glidepath of 3°. During the approach to Runway 09 at Liverpool all the anti-icing services were switched on and operating except for the wing de-icing boots which, having seen no ice on the wings,the commander decided not to employ, and the ice detector which he considered unreliable. The approach proceeded normally andthe aircraft descended out of cloud at about 1,100 feet having been in cloud for about 10 minutes. When the commander viewed the PAPIs at 1 DME"all four lights had a pink tinge". Thinking he might be slightly low relative to the approach glidepath, he asked the co-pilot to specify the correct height at 1 DME which was 410feet. At the time the commander's pressure altimeter, which was set to the QNH of 1019 mb, indicated that the aircraft was slightly high and so he made a small correction to the flight path which resulted in three red PAPI lights and one white light. The commander also decided to touch down slightly beyond the runway identifier numbers which are a few metres beyond the 'piano keys' that identify the threshold. The aircraft was cleared to land with a wind of "Easterly at 10 kt" and on short finals the commander asked for full flap. He then allowed the speed to bleed back from the approach speed of between 110 and 120 KIAS towards the threshold speed of 90 KIAS without moving the throttles from their approach power setting. According to both crew members and the passenger who was seated in the 'jump seat', the aircraft crossed over the end of runway at between 88 and 90 KIAS. Some 20 to 30 feet above the runway the commander noticed that the flight controls felt 'sloppy' as if the aircraft's speed was unusually low but there was no hint of a stall warning or stick shaker activation. At much the same time all three persons on board felt the aircraft sink rapidly; the commander pulled back on the control column but he was unable to arrest the high rate of descent and the aircraft struck the runway very hard. The right wing dropped as the right main gear collapsed and the aircraft veered to the right off the runway onto the grass. The ground was frozen hard and the aircraft came to a halt without incurring further significant damage. The crew informed ATC that they were unhurt before securing the aircraft whilst ATC activated the airport's emergency services. On leaving the aircraft the commander inspected the wings for ice accretion. He noticed a thin layer of clear,watery ice along the leading edges across the pneumatic de-icing boots from top to bottom. The ice layer could be wiped off with one finger and was no more than one eight of an inch thick. Throughout the flight there had been no visible signs of ice accretion on the wings or the windscreen wiper. Consequently, the commander had not increased the threshold speed to compensate for ice accretion.

During his weather briefing, the pilot was told that his destination weather was not available, and was provided weather for an airport about 10 miles north. He was briefed that low visibility due to fog prevailed. The flight departed earlier then usual because the company business manager was concerned that the weather at the destination airport was deteriorating, and if the airplane was not there earlier they might not get into the airport. At the time of the accident there was a power failure, and lights around the destination airport went out. The airplane had struck power lines and a support tower located on the approach end of runway 1 and runway 5, about 1/2 mile southwest of the airport. The airport had one NDB approach which was not authorized at night. The nearest recorded weather, about 10 miles north of the crash site, at the time of the accident was; '...ceiling 100, [visibility] 1/2 mile, fog, [temperature] 46 degrees F, dew point, 42 degrees F, winds 220 degrees at 5 [knots], altimeter 29.90 inches Hg. Witnesses reported that there was heavy fog at the airport and the visibility was below 1/4 mile.

There were five recorded transmissions of conversations from one of the pilots aboard the accident airplane and the Fort Dodge, Iowa AFSS; one on 12/27 and four on 12/28. The weather forecast for icing included wording such as '...moderate to isolated severe icing from seven thousand downward for your entire route of flight....' The pilot stated that he received 'Full Flight Service briefings...' and also indicated that he spoke to flight watch prior to takeoff. While executing the ILS approach to the destination airport, the pilot was unable to maintain the proper glidepath even with the application of full power. The pilot maintained marginal control of the airplane during the descent until impact with trees and the terrain about 10 miles west of the destination airport. The pilot and passengers reported 'vibration' and 'shudder' of the airplane prior to the impact. One passenger reported that she saw ice forming on the left 'rear' wings. Persons on the ground reported severe icing conditions around the time of the accident.

The first officer was in the left seat, flying the airplane, and the captain was in the right seat, for the positioning flight. Approaching the destination, the crew briefed, then attempted an ILS RWY 18 approach. The captain reported not receiving the localizer, when, in fact, the airplane was actually about 5 nautical miles to the left of it. Winds at the airport, about that time, were from 190 degrees true, at 5 knots; however, area winds at 6,000 feet were from 220 degrees, in excess of 40 knots. The crew executed a missed approach, but did not follow the missed approach procedures. The captain later requested, and received clearance for, the VOR RWY 25 approach. The captain partially briefed the approach to the first officer as the airplane neared the VOR, then subsequently "talked through" remaining phases of the approach as they occurred. The outbound course for the VOR RWY 25 approach was 066 degrees, and the minimum altitude outbound was 4,300 feet. After passing the VOR, the captain directed the first officer to maintain 4,700 feet. The airplane's last radar contact occurred as the airplane was proceeding outbound, 7 nautical miles northeast of the VOR, at 4,800 feet. As the airplane approached the course reversal portion of the procedure turn, the captain initially directed the first officer to turn the airplane in the wrong direction. When the proper heading was finally given, the airplane had been outbound for about 2 minutes. During the outbound portion of the course reversal, the captain told the first officer to descend the airplane to 2,900 feet, although the procedure called for the airplane to maintain a minimum of 4,300 feet until joining the inbound course to the VOR. During the inbound portion of the course reversal, the captain amended the altitude to 3,000 feet. As the airplane neared the inbound course to the VOR, the captain called out the outer marker. The first officer agreed, and the captain stated that they could descend to 2,300 feet. The first officer then noted that the VOR indications were fluctuating. The captain pointed out the VOR's continued reception, and the first officer noted, "but it's all over the place." Shortly thereafter, the first officer stated that he was descending the airplane to 2,300 feet. Three seconds later, the airplane impacted trees, then terrain. The wreckage was located at the 2,300-foot level, on rising mountainous terrain, 061 degrees magnetic, 12.5 nautical miles from the VOR. It was also 10.3 nautical miles prior to where a descent to 2,300 feet was authorized. There was no evidence that the crew used available DME information. There was also no evidence of pre-impact mechanical malfunction.

The approach to Nagurskoye Airport was completed by a polar night and in poor weather conditions with snow falls. After landing on an iced and snow covered runway, the aircraft overran, lost its undercarriage and came to rest. Nine occupants were injured, among them four seriously. The aircraft was damaged beyond repair.

The aircraft was completing a cargo flight from Bogotá to Medellín, carrying one passenger, three crew members and a load of 18,300 newspapers for a total weight of 4,970 kilos. While descending to Medellín-Rionegro Airport, the crew encountered difficulties to intercept the ILS and made successives left and right turn when, on final approach, the aircraft went out of control and crashed 8 km short of runway 36. All four occupants were killed.

While descending to Port Harcourt Airport, the pilot-in-command established a visual contact with the runway lights at an altitude of 2,500 feet. The approach was continued when few seconds later, while the crew was thinking his altitude was 390 feet, the aircraft collided with trees. The captain decided to initiate a go-around procedure but all four engines failed to respond properly. The aircraft continued to descend and struck the ground 250 metres short of runway threshold. Upon impact, the undercarriage were torn off and the aircraft slid for few dozen metres before coming to rest. All four crew members escaped uninjured and the aircraft was damaged beyond repair. It was reported that the aircraft was unstable on final approach.

The pilot had received clearance for the ILS Runway 6 approach and was advised that the previous landing traffic reported '...breaking out at minimums.' Radar data revealed that the airplane descended in instrument meteorological conditions to the decision height altitude of 294 feet, approximately 3 miles from the missed approach point. The pilot did not perform the missed approach procedure. The airplane leveled off and continued at or below decision height altitude for approximately 28 seconds, traveling a distance of approximately 1 mile. Four low altitude alerts appeared on the tower controller's display. The controller stated he withheld the alert because '...it was a critical phase of flight and the aircraft appeared to be climbing...' The airplane collided with trees and terrain approximately 1.5 miles from the approach end of the landing runway.