Northwest Airlines Flight 705

Northwest Airlines Flight 705
	An identical Boeing 720B from Northwest Airlines
Accident summary
Accident type	Loss of control and structural failure
place	Everglades , Florida United States
date	February 12, 1963
Fatalities	43
Survivors	0
Aircraft
Aircraft type	Boeing 720-051B
operator	Northwest Airlines
Mark	N724US
Departure airport	Miami International Airport , Florida , United States
1. Stopover	O'Hare International Airport , Illinois , United States
2. Stopover	Spokane International Airport , Washington , United States
3. Stopover	Seattle-Tacoma International Airport , Washington , United States
Destination airport	Portland International Airport , Oregon , United States
Passengers	35
crew	8th
	Lists of aviation accidents

Northwest Airlines Flight 705 (flight number: NW705 ) was a scheduled domestic flight operated by Northwest Airlines from Miami to Portland with stops in Chicago , Spokane and Seattle . On February 12, 1963, the Northwest Airlines Boeing 720-051B N724US crashed shortly after taking off from Miami Airport . The machine got out of control while flying through a severe thunderstorm, broke apart in mid-air and fell into the Everglades . All 43 inmates were killed.

plane

The machine was a Boeing 720-051B. The Boeing 720 was a further development of the long-haul aircraft of the Boeing 707 to a special short to medium-haul variant with a shortened fuselage. The aircraft used on Flight 705 was the 224th Boeing of the 707/720 series with the factory number 18354. This had made its first flight on April 17, 1962 and was then delivered to its first owner Northwest Airlines . The aircraft had the aircraft registration N724US . The four-engine medium range - narrow-body aircraft was equipped with four engines of the type Pratt & Whitney Jt3d-1 equipped. At the time of the accident, the machine was operating for 4685 hours.

the accident

On the day of departure there was a severe thunderstorm near Miami. Before the aircraft rolled from the gate to take-off, the pilots asked air traffic control which route they should fly when taking off. The air traffic controllers replied that most of the machines would climb either south-west or south-east and then turn around and fly over the storm.

The machine received clearance to take off from runway 27L (course 270 °, therefore in a westerly direction). According to the vectors that he had received from air traffic control, the captain Roy Almquist flew a left turn in order to avoid areas where storm-related turbulence was to be expected. Another machine had received the same instruction shortly before departure.

While the pilots now maintained an altitude of 5000 feet (approx. 1500 meters) and a south-easterly course, they were instructed to turn on a 300 ° course, i.e. northwest. They asked her permission to go to a higher flight level. While the pilots were talking to the air traffic controller about the storm activity and the request for permission to climb was coordinated with the control center in Miami, one of the pilots said, "Ahh, we are now out of the woods. We can see it ahead of us. Looks pretty bad. " ("Ah-h we're in the clear now. We can see it out ahead ... looks pretty bad."). The pilot was referring to the thunderstorm that was now clearly visible to the right in front of the aircraft.

At 1:43 p.m., the pilots were given clearance to climb to 25,000 feet (approx. 7,500 meters). They replied that they would make a left turn of about 30 degrees and then climb. The air traffic controller asked whether the course of 270 degrees resulting from the curve was the course on which the crew wanted to continue the flight, to which the pilots replied that they would fly such a course towards the storm again, with the intention of to fly over them. Air traffic control then gave the crew clearance to climb. After the pilots and air traffic controllers talked about the possible severity of the turbulence, which was described as moderate to severe, it was decided to avoid the thunderstorm.

At 1:45 p.m., the Miami Air Route Traffic Control Center took over flight 705. There were difficulties communicating, but no other radio frequency for which the aircraft was designed was switched. A few minutes after contact was made, the aircraft's rate of climb suddenly increased to 9,000 feet per minute, three times the usual rate of climb for this type of aircraft. The aircraft had reached a strong updraft zone as a result of the thunderstorm. Following this rapid ascent, during which the aircraft's airspeed dropped from 270 to 215 knots (500/398 km / h), and in response to the unintended high rate of climb, the pilot lowered the aircraft's nose sharply after a brief An altitude of 19,000 feet (about 6,000 meters) had been reached. As a result, the rate of climb dropped below zero and the plane began to descend rapidly. As a result of the now beginning dive, the negative vertical acceleration increased to about -2 G, so the aircraft now sank very quickly. This resulted in a stall , as the flow was now flowing diagonally from below, which massively increased the angle of attack.

Within the next seven seconds, the negative acceleration increased further to -2.8 G. With increasing speed, the machine began to fall almost vertically towards the ground. In these seven seconds, the flight recorder did not record any further control inputs, probably because both pilots were pushed into their seats by the descent and thus could not reach the controls. When the pilot managed to reach the controls, he was able to intercept the fall briefly by lifting the aircraft's nose with the elevator, the load multiple rose again to a positive value of 1.5 G. Due to the aerodynamic forces that occurred, however, a stable flight position could not be established. the machine lowered its nose again and dived again. The load multiple reached -3 G. The speed increased to at least 470 knots (870 km / h), the upper limit of the recording capability of the flight data recorder.

After the machine had sunk below 10,000 feet (approx. 3000 meters), the aircraft broke apart completely as a result of the extraordinary structural stress. The wreckage of the machine fell in an unpopulated area in Everglades National Park , 37 miles (60 kilometers) west-southwest of Miami Airport.

meaning

It was the first accident involving a Boeing 720 on a passenger flight and thus the most serious incident of this type. Two years later, the number of victims of the crash was exceeded by the historically most serious accident involving a Boeing 720: the accident on Pakistan International Airlines Flight 705 with 121 deaths was ironically carried out under the same flight number. This is also remarkable because in the entire operating time of the Boeing 720 there were only three fatal aircraft accidents in passenger flight operations.

Accident investigation

The aircraft accident investigation was conducted by the Civil Aeronautics Board . The final report found that the accident was caused by the unfavorable interaction of strong upwinds and downwashes and inappropriately strong rudder inputs by the pilots and the resulting changes in the pitch of the machine. As a result, the machine got into an attitude from which the machine could no longer be intercepted. In addition, the structural load limits of the machine were subsequently exceeded, whereupon it broke apart.

Sources and Links

Operational History B-707-138B, N791SA Jetphotos.com, accessed April 13, 2019.
Accident report in the Aviation Safety Network , accessed April 13, 2019.
Description of the incident and the underlying weather phenomena, map of the flight history and wreckage images , Federal Aviation Administration , accessed on April 13, 2019.

25.564819 -80.883408Coordinates: 25 ° 33 ′ 53 ″ N , 80 ° 53 ′ 0 ″ W.