Tag Archives: Clear Air Turbulence

5 March 1966

British Overseas Airways Corporation's Boeing 707-436 Intercontinental, G-APFE. (BOAC)
British Overseas Airways Corporation’s Boeing 707-436 Intercontinental, G-APFE. (British Airways)

5 March 1966: British Overseas Airways Corporation Speedbird 911, an around-the-world flight, departed Tokyo-Haneda Airport (HND) at 1:58 p.m., enroute Hong Kong-Kai Tak (HKG), with 113 passengers and 11 crew members. The airliner was a Boeing 707-436 Intercontinental, serial number 17706, with British registration G-APFE. It was nearly six years old, having been delivered 29 April 1960, and had 19,523 hours on the airframe.

Shortly before takeoff, the flight crew requested a change from an IFR flight plan to VFR, with a course that would take the airliner near Mount Fujiyama. The 707 climbed to an altitude of 16,000 feet (4,875 meters) as it approached the mountain from the southwest. The weather was very clear. A weather station on Mount Fuji recorded wind speeds of 60–70 knots (111–130 kilometers per hour).

Speedbird 911, Boeing 707 G-APFE, in a flat spin. The tail section and engines are missing, the right wing is broken and the airplane is trailing fuel vapor from ruptured tanks.
Speedbird 911, Boeing 707 G-APFE, in a flat spin. The tail section and engines are missing, the right wing is broken and the airplane is trailing fuel vapor from ruptured tanks. (JSDF)

Flying upwind toward Fujiyama at 320–370 knots (592–685 kilometers per hour), Speedbird 911 encountered severe Clear Air Turbulence that resulted in a catastrophic structural failure of the airframe. The vertical fin attachment failed and as it fell away, struck the left horizontal stabilizer, breaking it off. Next, the ventral fin and all four engine pylons failed due to extreme side loads. The 707 went in to a flat spin, trailing fuel vapor from ruptured tanks. The entire tail section broke away, the right wing failed, and the nose section came off.

The 707 left a debris field  that was 10 miles (16 kilometers) long. Speedbird 911 crashed in a forest on the lower flanks of Mount Fujiyama at about the 3,500 foot (1,066 meter) level. The forward section crashed about 1,000 feet (300 meters) away from the main wreckage. All 124 persons aboard were killed.

Disintegrating Speedbird 911 trails fuel vapor as it falls toward Mount Fujiyama, 5 March 1966.
Disintegrating Speedbird 911 trails fuel vapor as it falls toward Mount Fujiyama, 5 March 1966. (JSDF)

PROBABLE CAUSE: “The aircraft suddenly encountered abnormally severe turbulence over Gotemba City which imposed a gust load considerably in excess of the design limit.”

The accident was photographed by the Japanese Self Defense Forces from the East Fuji Maneuver Area, located in the foothills of the volcano. A passenger aboard Speedbird 911 had been filming with an 8 mm movie camera. The camera and film were recovered from the wreckage and the film was developed as part of the investigation. The film showed that the aircraft had experienced severe turbulence immediately before the accident. (Investigators estimated the peak acceleration at 7.5 g.)

A U.S. Navy Douglas A-4 Skyhawk was sent to look for the accident site. When the fighter approached Mount Fujiyama, it also encountered severe turbulence, to the point that the pilot feared the small fighter would break up in flight. After returning to base, the A-4 was grounded for inspection. Its accelerometer indicated that it had experienced acceleration forces ranging from +9 Gs to -4 Gs.

Mount Fujiyama, an active stratovolcano, i steh tallest mountain in Japan, at 12,389 feet (3,776.24 meters). It i sapproximately 62 miles (100 kilometers) southwest of Tokyo on the island of Hinshu.
Mount Fujiyama, an active stratovolcano, is the tallest mountain in Japan, at 12,389 feet (3,776.24 meters). It is approximately 62 miles (100 kilometers) southwest of Tokyo on the island of Honshu. (Alpsdake)

G-APFE was a Boeing 707-436 International, built in 1960 for British Overseas Airways. At the time of the accident, it had made 6,744 flights and accumulated a total of 19,523:33 hours (TTAF).

The -436 was a stretched version of the original 707-120, but with Rolls-Royce Conway 508 bypass turbojet engines (now called turbofans) in place of the standard Pratt & Whitney JT3C-6 turbojet engines. 15 ordered by British Overseas Airways Corporation in 1956.

The fuselage and wings of the Intercontinental were lengthened, allowing an increased load and greater fuel capacity. It could carry 189 passengers and had a range 1,600 miles further than the -120. Transoceanic flights without an intermediate fuel stop were possible.

Initially, British aviation authorities refused to certify the -436 because of low-speed handling concerns. Boeing increased the height of the vertical fin 40 inches and added a ventral fin. These modifications became standard on all future 707s and were retro-fitted to those already manufactured.

The Boeing 707-420 series airliners were 152 feet, 11 inches (46.609 meters) long, with a wingspan of 142 feet, 5 inches (43.409 meters) and overall height 42 feet, 2 inches (12.852 meters) at its operating empty weight. The leading edges of the wings and tail surfaces are swept 35°. The fuselage has a maximum diameter of 12 feet, 8.0 inches (3.759 meters). The 707 International has a typical empty weight of 142,600 pounds (64,682 kilograms), and a maximum takeoff weight (MTOW) of 312,000 pounds (141,700 kilograms). The usable fuel capacity is 23,820 gallons (90,169 liters).

British Overseas Airways corporation Boeing 707-436 International G-APFE photographed at Idlewild Airport, 27 June 1962. (Jon Proctor)

All 707-series aircraft are powered by four jet engines installed in nacelles below and forward of the wings on pylons. The -420 Internationals were powered by Rolls-Royce Conway Mk. 508 engines. The Rolls-Royce Conway (R.Co.12) is a two-spool, axial-flow, low-bypass turbofan engine. The engine has a 7-stage low- and 9-stage high-pressure compressor section, 12 interconnected combustion liners, with a single-stage high- and 2-stage low-pressure turbine. The Mk. 508 has a Maximum Continuous Power rating of 14,625 pounds of thrust (65.055 Kilonewtons), and 17,500 pounds of thrust (77.844 Kilonewtons) at 9,990 r.p.m., for Takeoff. The engine is 3 feet, 6.0 inches (1.067 meters) in diameter, 11 feet, 4.0 inches (3.454 meters) long, and weighs 4,542 pounds (2,060 kilograms).

The -420 series had a maximum cruise speed of 593 miles per hour 954 kilometers per hour) at 30,000 feet (9,144 meters)—0.87 Mach; and economical cruise speed of 550 miles per hour (885 kilometers per hour) at 35,000 feet (10668 meters).

Boeing built 1,010 Model 707 airplanes between 1957 and 1979. Of these, 37 were the 707-420 Intercontinental variant.

A British Overseas Airways Corporation Boeing 707-420-series International airliner, similar in appearance to G-APFE. (Travell Update)

© 2019, Bryan R. Swopes

Facebooktwittergoogle_plusredditpinterestlinkedinmailby feather

10 January 1964

Boeing B-52H-170-BW 61-023
Boeing B-52H-170-BW Stratofortress 61-023. (U.S. Air Force)

10 January 1964: This Boeing B-52H Stratofortress, serial number 61-023, flown by Boeing test pilot Charles F. (“Chuck”) Fisher, was conducting structural testing in turbulence near East Spanish Peak, Colorado. The other crew members were pilots Richard V. Curry and Leo Coer, and navigator James Pittman. Dick Curry was flying the airplane and Chuck Fisher, the aircraft commander, was in the co-pilot’s position. Pittman was on the lower deck.

The bomber was carrying two North American Aviation GAM-77 Hound Dog cruise missiles on pylons under its wings.

The Boeing B-52 Stratofortress had been designed as a very high altitude penetration bomber, but changes in Soviet defensive systems led the Strategic Air Command to change to very low altitude flight as a means of evading radar. This was subjecting the airframes to unexpected stresses. “Ten-Twenty-Three” (its serial number was 61-023, shortened on the vertical fin to “1023”) had been returned to Boeing Wichita by the Air Force to be instrumented to investigate the effects of high-speed, low-altitude flight on the 245-ton bomber.

Flying at 14,300 feet (4,359 meters) and 345 knots (397 miles per hour, 639 kilometers per hour), indicated air speed, the airplane encountered severe clear air turbulence and lost the vertical stabilizer. Several B-52s had been lost under similar circumstances. (Another, a B-52D, was lost just three days later at Savage Mountain, Maryland.)

East Spanish Peak (left), 12,688 feet (3,867 meters) and West Spanish Peak, 13,626 feet (4,153 meters), Sangre de Cristo Mountains, Colorado. (Footwarrior)
East Spanish Peak (left), 12,688 feet (3,867 meters) and West Spanish Peak, 13,626 feet (4,153 meters), Sangre de Cristo Mountains, Colorado. (Footwarrior)
Charles F. Fisher. (Argenta Images)
Charles F. Fisher. (Argenta Images)

Chuck Fisher immediately took control of the B-52. He later reported,

“As the encounter progressed, a very sharp-edged blow which was followed by many more. We developed an almost instantaneous rate of roll at fairly high rate. The roll was to the far left and the nose was swinging up and to the right at a rapid rate. During the second portion of the encounter, the airplane motions actually seemed to be negating my control inputs. I had the rudder to the firewall, the column in my lap, and full wheel, and I wasn’t having any luck righting the airplane. In the short period after the turbulence I gave the order to prepare to abandon the airplane because I didn’t think we were going to keep it together.”

A Boeing report on the incident, based on installed sensors and instrumentation aboard -023, said that the bomber had

“. . . flown through an area containing the combined effects of a (wind) rotor associated with a mountain wave and lateral shear due to airflow around a mountain peak. . . Gust initially built up from the right to a maximum of about 45 feet per second [13.7 meters per second] (TAS), then reversed to a maximum of 36 feet per second [11 meters per second] from the left, before swinging to a maximum of about 147 feet per second [44.8 meters per second] from the left followed by a return to 31 feet per second [9.5 meters per second].”

Fisher flew the bomber back to Wichita and was met by a F-100 Super Sabre chase plane. When the extent of the damage was seen, the B-52 was diverted due to the gusty winds in Kansas. Six hours after the damage occurred, Chuck Fisher safely landed the airplane at Eaker Air Force Base, Blythville, Arkansas. He said it was, “the finest airplane I’ve ever flown.”

Boeing B-52H-170-BW Stratofortress 61-023, "Ten-Twenty-Three", after losing the vertical fin, 10 January 1964. (Boeing)
Boeing B-52H-170-BW Stratofortress 61-023, “Ten-Twenty-Three”, after losing the vertical fin, 10 January 1964. (Boeing)

61-023 was repaired and returned to service. It remained active with the United States Air Force until it was placed in storage at Tinker Air Force Base, Oklahoma, 24 July 2008.

Charles F. Fisher and the Boeing test crew with B-52H Stratofortress 61-023. (Boeing)
Charles F. Fisher at left,  and the Boeing test crew with B-52H Stratofortress 61-023. (Boeing)

The B-52H is a sub-sonic, swept wing, long-range strategic bomber. It has a crew of five. The airplane is 159 feet, 4 inches (48.6 meters) long, with a wing span of 185 feet (56.4 meters). It is 40 feet, 8 inches (12.4 meters) high to the top of the vertical fin. Maximum Takeoff Weight (MTOW) is 488,000 pounds (221,353 kilograms).

There are eight Pratt & Whitney TF33-PW-3 turbofan engines mounted in two-engine pods suspended under the wings on four pylons. Each engine produces a maximum of 17,000 pounds of thrust (75.620 kilonewtons). The TF-33 is a two-spool axial-flow turbofan engine with 2 fan stages, 14-stage compressor stages (7 stage intermediate pressure, 7 stage high-pressure) and and 4-stage turbine (1 stage high-pressure, 3-stage low-pressure). The engine is 11 feet, 10 inches (3.607 meters) long, 4 feet, 5.0 inches (1.346 meters) in diameter and weighs 3,900 pounds (15,377 kilograms).

The B-52H can carry approximately 70,000 pounds (31,750 kilograms) of ordnance, including free-fall bombs, precision-guided bombs, thermonuclear bombs and cruise missiles, naval mines and anti-ship missiles.

The bomber’s cruise speed is 520 miles per hour (837 kilometers per hour) and its maximum speed is 650 miles per hour (1,046 kilometers per hour) at 23,800 feet (7,254 meters) at a combat weight of 306,350 pounds. Its service ceiling is 47,700 feet (14,539 meters) at the same combat weight. The unrefueled range is 8,000 miles (12,875 kilometers).

With inflight refueling, the Stratofortress’s range is limited only by the endurance of its five-man crew.

The B-52H is the only version still in service. 102 were built and as of 27 September 2016, 76 are still in service. Beginning in 2013, the Air Force began a fleet-wide technological upgrade for the B-52H, including a digital avionics and communications system, as well as an internal weapons bay upgrade. The bomber is expected to remain in service until 2040.

Boeing B-52H-170-BW Stratofortress 61-023 taxiing at Minot Air Force Base, North Dakota. (Senior Airman Cassandra Jones, U.S. Air Force)
Boeing B-52H-170-BW Stratofortress 61-023 taxiing at Minot Air Force Base, North Dakota. (Senior Airman Cassandra Jones, U.S. Air Force)

© 2016, Bryan R. Swopes

Facebooktwittergoogle_plusredditpinterestlinkedinmailby feather