Mountains

The commercial pilot was conducting a 1-hour commercial air tour flight over Denali National Park and Preserve with four passengers on board. About 48 minutes after departure, the Alaska Rescue Coordination Center received an alert from the airplane's emergency locator transmitter. About 7 minutes later, company personnel received a call from the pilot, who reported that the airplane had run "into the side of a mountain." Although a search was initiated almost immediately, due to poor weather conditions in the area, the wreckage was not located until almost 36 hours later in a crevasse on a glacier about 10,920 ft mean sea level. Due to the unique challenges posed by the steepness of terrain, the crevasse, avalanche hazard, and the condition of the airplane, neither the occupants nor the wreckage were recovered from the accident site. A weather model sounding for the area of the accident site estimated broken cloud bases at 700 ft above ground level (agl) with overcast clouds at 1,000 ft agl and cloud tops to 21,000 ft agl and higher clouds above. The freezing level was at 9,866 ft and supported light-to-moderate rime type icing in clouds and precipitation. The on-scene assessment indicated that the right wing impacted snow while the airplane was flying in a wings-level attitude; the right wing had separated from the remainder of the wreckage. Based upon available weather data and forecast models and the impact evidence, it is likely that the pilot entered an area of reduced visibility and was unable to see the terrain before the airplane's right wing impacted the snow. The company's organizational structure was such that one group of management personnel oversaw operations in both Anchorage and Talkeetna. Interviews with company management revealed that they were not always aware of the exact routing a pilot would take for a tour; the route was pilot's discretion based upon the weather at the time of the flight to provide the best tour experience. Regarding risk mitigation, the company did not utilize a formal risk assessment process, but rather relied on conversations between pilots and flight followers. This could lead to an oversight of actual risk associated with a particular flight route and weather conditions. About 8 months after the accident, an assessment flight conducted by the National Park Service determined that during the winter, the hazardous hanging glacier at the accident site calved, releasing an estimated 4,000 to 6,000 tons of ice and debris. There was no evidence of the airplane wreckage near the crash site, in the steep fall line, or on the glacier surface over 3,600 ft below. Although the known circumstances of the accident are consistent with a controlled flight into terrain event, the factual information available was limited because the wreckage was not recovered and no autopsy or toxicology of the pilot could be performed; therefore, whether other circumstances may have contributed to the accident could not be determined.

At 16:14 on 4 August 2018, the historic Junkers Ju 52/3m g4e commercial aircraft, registered as HB-HOT and operated by Ju-Air, took off from Locarno Aerodrome (LSZL) for a commercial VFR flight to Dübendorf (LSMD). On this flight, pilot A was sitting in the left-hand seat in the cockpit and piloting the aircraft as the commander, while pilot B was assisting him as the co-pilot sitting on the right. Following take-off from concrete runway 26R westwards and a 180-degree turn over Lake Maggiore, the flight led into the Blenio valley via Bellinzona and Biasca. HB-HOT steadily gained altitude in the process. North of Olivone, the aircraft turned into the valley of the Lago di Luzzone reservoir and thus into the Adula/Greina/Medels/Vals countryside preservation quiet zone. This zone was crossed at between 120 and 300 m above ground and at times with a minimal lateral separation from the terrain. At 16:45, as the aircraft was flying over Alp Nadels, the ISP sent a text message to a friend in Ruschein (municipality of Ilanz) to say that the Ju 52 was approaching the area. The flight subsequently continued eastwards into the Surselva region at approximately 2,500 m AMSL. At 16:51, the aircraft crossed the Vorderrhein valley in the region of Ilanz on a north-easterly heading and initially made a relatively tight left turn, taking it over Ruschein. The flight path then led generally northwards past the Crap Sogn Gion mountain and towards the basin south-west of Piz Segnas. At first, the aircraft approached this basin on the left-hand, western side of the valley. HB-HOT was climbing at this time, and reached an altitude of 2,833 m AMSL in the Nagens region. The aircraft made a slight right turn when flying past the Berghaus Nagens lodge (see figure 2). During this phase, at 16:55, one of the pilots informed the passengers of the scenery over the speakers in the cabin and through the passengers’ personal headphones. To start with, the aircraft was flying at a ground speed of 165 km/h during this phase. By point F2, the ground speed had decreased to 135 km/h, and roughly remained so until shortly before point F3. Towards point F3, the aircraft’s altitude dropped slightly and the ground speed briefly increased by around 65 km/h to approximately 200 km/h. During this time, its pitch attitude3 was 5 to 7 degrees. Towards the end of this phase, just before point F4, the flight path angle4 changed from -3 degrees to approximately -1 degree and the speed of each of the three engines decreased steadily by approximately 20 revolutions per minute (rpm). At point F4, the aircraft was at an altitude of 2,742 m AMSL. At 16:56:02, shortly after point F4, the speed of each of the three engines increased by approximately 40 rpm. At 16:56:09, HB-HOT entered the basin southwest of Piz Segnas at an altitude of 2,755 m AMSL (point F5, see also figure 14) and was therefore approximately 130 m above the elevation of the Segnes pass. The flight crew then navigated the aircraft on a north-north-easterly heading almost in the centre of the valley. HB-HOT climbed slightly during this phase and its flight path angle was approximately 2 degrees; its pitch angle remained at 5 to 7 degrees. At 16:56:17, the aircraft reached an altitude of 2,767 m AMSL at point F7 and was therefore approximately 140 m above the elevation of the Segnes pass. HB-HOT flew past the Tschingelhörner mountain peaks and began to reduce in altitude, dropping more than 15 m in approximately 6 seconds. During this phase, the power of the engines was rapidly reduced by 30 to 50 rpm, which meant that the engines were increasingly running at a similar speed5 . During this process, the pitch angle increased and the flight path angle continuously became more negative. When the aircraft was approximately abeam the Martinsloch and at an altitude of approximately 2,766 m AMSL (point F8), the flight crew initiated a right turn during their descent and then made a left turn (point F109, see figure 5). The ground speed was approximately 170 km/h and the difference between the aircraft’s pitch and flight path angles increased to approximately 15 degrees during the right turn. When transitioning into the left turn (between points F9 and F10), the pitch angle was approximately 11 degrees and the flight path angle was around -10 degrees. At this time, the aircraft was flying at approximately 125 m above the elevation of the Segnes pass (see figure 3). During roughly the next 4 seconds, the aircraft descended by 25 m and the already negative flight path angle became even more negative, which is clearly apparent when comparing figures 3 and 4 as well as in figure 5. After point F13, the roll to the left increased steadily and did not decrease even when a significant aileron deflection to the right was made. The ailerons were then brought into a neutral position and temporarily deflected into a position for a left turn. At the same time, the pitch attitude began to decrease and the flight path ran increasingly steeper downwards whilst the left bank attitude constantly increased (see figure 6). During this last flight phase, the aircraft experienced low-frequency vibrations. Ultimately, when the aircraft was 108 m above ground (point F16, see figures 6 and 7), its longitudinal axis was pointing downwards by 68 degrees from horizontal. By this time, the elevator had deflected upwards by approximately 13 degrees and the rudder was pointing 2 degrees to the right. The speeds of the three engines had increased slightly compared to the beginning of the downward spiral trajectory and were between 1,720 and 1,750 rpm shortly before impact. The roll to the left accelerated significantly during this phase. Shortly after 16:57, the aircraft hit the ground in a vertical flight attitude with an almost vertical flight path and at a speed of approximately 200 km/h (see figure 8). All 20 people on board the aircraft lost their lives in the accident. The aircraft was destroyed. Fire did not break out. Reconstructions revealed that, at the time of the accident, HB-HOT’s centre of gravity was at 2.071 m behind the wing’s leading edge (see annex A1.6). In the images and video footage available that had been captured from inside HB-HOT, there was no evidence of anyone moving within the aircraft or not sitting in their seat between the period when the aeroplane entered the basin south-west of Piz Segnas and up to the beginning of its downward spiral trajectory. A detailed description of the reconstruction of the flight path and an illustration of the relevant parameters between position F1 and the site of the accident can be found in section 1.11.2. More information regarding the background and history of the flight can be found in annex A1.1.

On 01 August 2018, after completing 2 hours of survey work near Penticton, British Columbia (BC), an Aries Aviation International Piper PA-31 aircraft (registration C-FNCI, serial number 31-8112007) proceeded on an instrument flight rules flight plan from Penticton Airport (CYYF), BC, to Calgary/Springbank Airport (CYBW), Alberta, at 15 000 feet above sea level. The pilot and a survey technician were on board. When the aircraft was approximately 40 nautical miles southwest of CYBW, air traffic control began sequencing the aircraft for arrival into the Calgary airspace and requested that the pilot slow the aircraft to 150 knots indicated airspeed and descend to 13 000 feet above sea level. At this time, the right engine began operating at a lower power setting than the left engine. About 90 seconds later, at approximately 13 500 feet above sea level, the aircraft departed controlled flight. It collided with terrain near the summit of Mount Rae at 1336 Mountain Daylight Time. A brief impact explosion and fire occurred during the collision with terrain. The pilot and survey technician both received fatal injuries. The Canadian Mission Control Centre received a 406 MHz emergency locator transmitter signal from the occurrence aircraft and notified the Trenton Joint Rescue Coordination Centre. Search and rescue arrived on site approximately 1 hour after the accident.

The airline transport pilot was conducting a commercial visual flight rules (VFR) flight transporting 10 passengers from a remote fishing lodge. According to the pilot, while in level cruise flight about 1,100 ft mean sea level (msl) and as the flight progressed into a mountain pass, visibility decreased rapidly. In an attempt to turn around and return to VFR conditions, the pilot initiated a climbing right turn. Before completing the 180° right turn, he saw what he believed to be a body of water and became momentarily disoriented, so he leveled the wings. Shortly thereafter, he realized that the airplane was approaching an area of snow-covered mountainous terrain, so he applied full power and initiated a steep climb; the airspeed decayed, and the airplane collided with an area of rocky, rising terrain, which resulted in substantial damage to the wings and fuselage. The pilot reported no mechanical malfunctions or anomalies that would have precluded normal operation, and the examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. The weather forecast at the accident time included scattered clouds at 2,500 ft msl, overcast clouds at 5,000 ft msl with cloud tops to 14,000 ft and clouds layered above that to flight level 250, and isolated broken clouds at 2,500 ft with light rain. AIRMET advisory SIERRA for "mountains obscured in clouds/precipitation" was valid at the time of the accident. Conditions were expected to deteriorate. Passenger interviews revealed that through the course of the flight, the airplane was operating in marginal visual meteorological conditions and occasional instrument meteorological conditions (IMC) with areas of precipitation, reduced visibility, obscuration, and, at times, little to no forward visibility. Thus, based on weather reports and forecasts, and the pilot's and passengers' statements, it is likely that the flight encountered IMC as it approached mountainous terrain and that the pilot then lost situational awareness. The airplane was equipped with a terrain awareness and warning system (TAWS); however, the alerts were inhibited at the time of the accident. Although the TAWS was required to be installed per Federal Aviation Administration (FAA) regulations, there is no requirement for it to be used. All company pilots interviewed stated that the TAWS inhibit switch remained in the inhibit position unless a controlled flight into terrain (CFIT) escape maneuver was being accomplished. However, the check airman who last administered the accident pilot's competency check stated that the TAWS inhibit switch was never moved, even during a CFIT escape maneuver. The unwritten company policy to leave the TAWS in the inhibit mode and the failure of the pilot to move the TAWS out of the inhibit mode when weather conditions began to deteriorate were inconsistent with the goal of providing the highest level of safety. However, if the pilot had been using TAWS, due to the fact that he was operating at a lower altitude and thus would have likely received numerous nuisance alerts, the investigation could not determine the extent to which TAWS would have impacted the pilot's actions. At the time of the accident, the director of operations (DO) for the company resided in another city and served as DO for another air carrier as well. He traveled to the company's main base of operation about once per month but was available via telephone. According to the chief pilot, he had assumed a large percentage of the DO's duties. The president of the company said that the chief pilot had taken over "officer of the deck" and "we're just basically using him [the DO] for his recordkeeping." The FAA was aware that the company's DO was also DO for another commuter operation. FAA Flight Standards District Office management and principal operations inspectors allowed him to continue to hold those positions, although it was contrary to the guidance provided in FAA Order 8900.1. The company's General Operations Manual (GOM) only listed the DO, the chief pilot, and the president by name as having the authority to exercise operational control. However, numerous company personnel stated that operational control could be and was routinely delegated to senior pilots. The GOM stated that the DO "routinely" delegated the duty of operational control to flight coordinators, but the flight coordinator on duty at the time of the accident stated that she did not have operational control. In addition, the investigation revealed numerous inadequate and missing operational control procedures and processes in company manuals and operations specifications. Based on the FAA's inappropriate approval of the DO, the insufficient company onsite management, the inadequate operational control procedures, and the exercise of operational control by unapproved persons likely resulted in a lack of oversight of flight operations, inattentive and distracted management personnel, and a loss of operational control within the air carrier. However, the investigation could not determine the extent to which any changes to operational control, company management, and FAA oversight would have influenced the pilot's decision to continue the VFR flight into IMC.

The twin engine airplane was carrying two technicians and two pilots bound for a mine field located near Lero, Kankan. It made an intermediate stop at Conakry on a flight from Sal, Cape Verde. En route, the crew encountered poor weather conditions with low clouds and fog when the airplane struck the slope of a mountain and disintegrated on impact. All four occupants were killed.

The aircraft took-off from Kitale Airstrip (HKKT) at 16.05 hours and set course to Jomo Kenyatta International Airport (HKJK) after climbing to FL 110 with ten onboard. Once established, there were slight peripheral variations in groundspeed and track. The aircraft Flight Level was sustained at 110 with some occasional deviations. Aircraft height above ground level (AGL) varied between 1,102 feet and 4,187 feet. One minute before its impact with the cliff, the aircraft was at 11,100 feet or 3,000 feet AGL, 159 knots ground speed, and tracking radial 338 NV. Immediately before radar signal was lost, the elevation of the highest ground level was 12,876 feet, the aircraft altitude was 11,200 feet, the ground speed was 156 knots, and track was radial 339 NV. Information retrieved from the Radar transcript recorded various parameters of the aircraft from 1605hrs up to 1702hrs, the time radar signal was lost. This information was consistent with information extracted from the on-board equipment the ST3400 and the aera GPS. The radar system transmits information including aircraft position in relation to NV VOR, Flight Level or altitude, ground speed, vertical speed and heading. Information retrieved from the GPS captured the last recorded time, date and location as 14:00:52, on 06/05/2018 and elevation 3,555.57 metres. The aircraft impacted the bamboo-covered terrain at an elevation of 3,645 metres at 0.36’56’’S 36 42’44’’ where the wreckage was sited. The aircraft was totally destroyed by impact forces and all 10 occupants were killed.

The single engine aircraft departed Surkhet Airport at 0612LT on a cargo flight to Simikot. At 0627LT, the crew made his last radio transmission with Nepalgunj Tower. About 18 minutes later, while cruising by night at an altitude of 12,800 feet, the airplane struck the slope of a mountain located near the Simikot Pass, some 12 km from Simikot Airport. The airplane disintegrated on impact and both crew members were killed.

The single engine aircraft crashed in unknown circumstances in a wooded and hilly terrain located near Tuzantán. The airplane was totally destroyed by a post crash fire and all three occupants were killed. According to Mexican Authorities, the crew was completing an illegal flight.

A Turkish Challenger 604 corporate jet impacted a mountain near Shahr-e Kurd in Iran, killing all 11 on board. The aircraft departed Sharjah, UAE at 13:11 UTC on a flight to Istanbul, Turkey. The aircraft entered Tehran FIR fifteen minutes later and the Tehran ACC controller cleared the flight to climb to FL360 according to its flight plan. About 14:32, the pilot requested FL380, which was approved. Before reaching that altitude, the left and right airspeeds began to diverge by more than 10 knots. The left (captain's) airspeed indicator showed an increase while the right hand (copilot's) airspeed indicator showed a decrease. A caution aural alert notified the flight crew of the difference. Remarks by the flight crew suggested that an 'EFIS COMP MON' caution message appeared on the EICAS. As the aircraft was climbing, the crew reduced thrust to idle. Approximately 63 seconds later, while approaching FL380, the overspeed aural warning (clacker) began to sound, indicating that the indicated Mach had exceeded M 0.85. Based on the Quick Reference Handbook (QRH) of the aircraft, the pilot flying should validate the IAS based on the aircraft flight manual and define the reliable Air Data Computer (ADC) and select the reliable Air Data source. The pilot did not follow this procedure and directly reduced engine power to decrease the IAS after hearing the clacker. The actual airspeed thus reached a stall condition. The copilot tried to begin reading of the 'EFIS COMP MON' abnormal procedure for three times but due to pilot interruption, she could not complete it. Due to decreasing speed, the stall aural warning began to sound, in addition to stick shaker and stick pusher activating repeatedly. The crew then should have referred to another emergency procedure to recover from the stall condition. While the stick pusher acted to pitch down the aircraft to prevent a stall condition, the captain was mistakenly assumed an overspeed situation due to the previous erroneous overspeed warning and pulled on the control column. The aircraft entered a series of pitch and roll oscillations. The autopilot was disengaged by the crew before stall warning, which ended the oscillations. Engine power began to decrease on both sides until both engines flamed out in a stall condition. From that point on FDR data was lost because the electric bus did not continue to receive power from the engine generators. The CVR recording continued for a further approximately 1 minute and 20 seconds on emergency battery power. Stall warnings, stick shaker and stick pusher activations continued until the end of the recording. The aircraft then impacted mountainous terrain. Unstable weather conditions were present along the flight route over Iran, which included moderate up to severe turbulence and icing conditions up to 45000ft. These conditions could have caused ice crystals to block the left-hand pitot tube. It was also reported that the aircraft was parked at Sharjah Airport for three days in dusty weather condition. Initially the pitot covers had not been applied. The formation of dust inside the pitot tube was considered another possibility.

Iranian ATR72 aircraft registered EP-ATS operated by Iran Aseman Airlines was assigned to perform a domestic scheduled passenger flight from Tehran to Yasuj on 07:55 local time. The aircraft took off from Tehran Mehrabad International Airport (0III) at 04:35 UTC. (08:05 LMT) and the flight was the first flight of the day for aircraft and the crew. The cruise flight was conducted at FL210 on airway W144 and no abnormal situation was reported by the crew and the flight was continued on Tehran ACC frequency till the time the first officer requested latest weather information of the destination by contact to Yasuj tower then requested to leave FL210 to FL170 from Tehran ACC. When the aircraft was descending to FL170 and crew calling YSJ tower the aircraft descending was continued to altitude of 15000 ft. The aircraft was approved to join overhead of the airport and perform “circling NDB approach “to land on RWY 31 at the destination aerodrome. Finally the aircraft collided with a peak lee of DENA Mountains about 8.5 miles at North far from the airport and involved accident on 06:01 UTC. The aircraft was completely destroyed as a result of collision with the mountain at the altitude of approximately 13,300 ft.