Independent Air Flight 1851

On 8 February 1989, Independent Air Flight 1851, a Boeing 707 on an American charter flight from Bergamo, Italy, to Punta Cana, Dominican Republic, struck Pico Alto while on approach to Santa Maria Airport in the Azores for a scheduled stopover. The aircraft was destroyed, with the loss of all 144 people on board, resulting in the deadliest plane crash in Portugal's history. All of the passengers on board were Italian and all of the crew were Americans. The crash is also known as "The disaster of the Azores" (Il disastro delle Azzorre).

Accident

Flight 1851 had communication difficulties with air traffic controllers at high frequencies (HF), although it worked without failures on the ground. At 12:46:33, the crew contacted the Santa Maria Air Traffic Control center and reported on the passage point. Flight 1851 was handled by a trainee air traffic controller. As the investigators later noted, phraseology was violated during the communications. The controller also used the word "point" instead of "decimal", meaning a decimal point. Radio communication with the land was conducted mainly by first officer Adcock, with the exception at 13:43:57 when flight engineer Gonzalez requested a weather report. At 13:44:20 the controller transmitted: "One eight five one wind two six zero... Fourteen ah fourteen knots maximum two four knots visibility more than ten kilometers one octa at one two zero zero feet six octa at three thousand feet ah temperature one seven QNH one zero one niner." During the transmission, the controller used non-standard terminology "at" in the sentence, "one octant for one two zero zero." Due to the communication difficulties, the crew heard the message as "one octant two two zero zero," from which they falsely determined that there were no clouds below 2,000 feet.

At 13:56:47, when flight 1851 was performing a descent to the airfield and passing 6705 m, the controller dispatched: "Independent Air one eight five one roger you're cleared to three thousand feet on QNH one zero two seven and ah runway will be one niner." The controller made a major error during this transmission. He had reported to the crew the pressure of 1027 hPa, when it was actually 1018.7, (rounded 1018), which is 9 hPa lower. The instructor noticed this and wanted to transmit the correct information to the crew, but he was distracted by a phone call. Also, the crew members themselves failed to notice the transfer of high pressure, which 12 minutes earlier was much lower. This could have been facilitated by the presence of a flight attendant in the cockpit, whose voice was recorded by the Cockpit Voice Recorder (CVR) at 13:48:30 and at 14:04:09.

At 13:56:59 the co-pilot told the controller: "We're cleared to two thousand feet and ah...," but paused mid-sentence at 13:57:02. At that same time Daugherty said, "Make it three [thousand]." Then 13:57:07 Adcock continued his radio transmission: "one zero two seven." This was the last transmission from Flight 1851, but the controller did not hear the first part, as he continued to say that the flight would be landing on runway 19, and therefore did not know that the plane continued to descend to 2000 ft. As this was below the minimum safe altitude of 3,000 ft, the aircraft was flying straight to the mountain.

At 14:02, at a speed of 260 kn, the plane passed a height of 5000 ft and got into a zone of light turbulence. At 14:03 Adcock stated, "Ah after two thousand yeah we'll get below these clouds." At 14:06 at a speed of 250 kn, and at a height of 2000 ft the aircraft encountered heavy turbulence near Santo Espírito, with Daugherty saying at 14:07:52, "Can't keep this son of a bitch thing straight up and down." Adcock asked Daugherty if he needed help, but he replied, "no." Then at 14:08:00 due to the turbulence, the aircraft climbed sharply from 1751 ft to 1869 ft. As a result radio altimeter then gave a warning signal and then the Ground Proximity Warning System (GPWS) activated, sounding several "whoop whoop pull up" audible alarms, but the crew did not respond to warnings.

At 14:08:12, at an actual altitude of 1795 ft above sea level, the aircraft crashed into a wall by a road, skidded through trees with trunks about 30 - 40 cm in diameter, and exploded. The impact occurred on the east side of the mountain. The majority of debris was on this side of the mountain, though several portions of debris were also found on the western slope of the mountain as the initial impact site was near the summit. All 144 people (7 crew members and 137 passengers) on board were killed. This is the deadliest aviation disaster to occur in Portugal and the fourth deadliest involving a Boeing 707.