A History of Boeing 720 Aircraft AccidentsDecember 21, 2022
The Boeing 720 was involved in incidents far worse than hijackings, although only two of them in the 15-year period from 1960 to 1974 entailed fatalities.
The earliest recorded 720 incident took place on December 4, 1960 on board a United Airlines 720-022 carrying seven crew members and 84 passengers. The flight penetrated an area of severe turbulence over Wolbach, Nebraska, resulting in injuries in the cabin. It was later determined that the captain had failed to display adequate precaution before he entered the turbulent area.
Another non-fatal 720 incident occurred the following year, on February 25, when a Braniff 720-027 with seven crew members and 24 passengers executed a hard landing short of the runway in Houston. While there was no loss of life, the aircraft sustained major damage. The cause was determined to be pilot misjudgment.
Yet another 720 landing incident took place later that year, on September 24, 1961, when the captain of an American Airlines 720-023B that carried 33 passengers and seven other crew members elected to execute a landing in Boston during varying weather conditions, but he was not advised of rapidly decreasing runway visual range (RVR). He also committed the airliner to land before receiving sufficient information concerning the location of such conditions relative to the runway.
The first fatality-producing Boeing 720 accident took place on February 12, 1963 on board a Northwest Orient 720-051B, registered N724US, about to embark on a nonstop flight from Miami to Chicago-O’Hare. A fierce storm, creating dark skies, hovered over Southern Florida that day and all arriving flights were diverted because of it. An Eastern 720-025 delayed its takeoff until conditions improved.
Northwest Flight NW 705, scheduled to depart at 1:30 p.m., was piloted by Captain Roy W. Almquist, 47, First Officer Robert J. Feller, 38, and Second Officer Allen R. Friesen, 29, and five flight attendants were to serve the 35 passengers in the cabin.
Aware of the raging weather system, Almquist believed he could execute a safe departure by taking off to the west and then banking southwest, circling around the area of greatest activity. Intense storm cells were now both west and northwest of the airport. As a result, departing flights were being given an initial southwest or southeast route, followed by the proper westerly or northwesterly track once they had gained sufficient altitude to overfly the storm. Flight 705 intended to follow the same path.
The gleaming, factory-fresh jetliner, operating Northwest Orient’s Regal Imperial Service, taxied from the gate beneath almost-black skies, amid gale winds that socked the aircraft and shock it even on the ground.
After aligning with Runway 27-Left’s centerline, it accelerated and rotated into a 25-knot wind, divorcing itself from Florida soil and establishing a positive rate-of-climb over the Palmetto Expressway. Initially cleared to ascend and maintain 3,000 feet, it banked and assumed a south-southwesterly heading. Miami Departure Control further granted it permission to ascend and maintain 5,000 feet on a modified southwesterly heading, which took it over Homestead, Florida, where mighty, menacing cumulous clouds loomed off the starboard side.
Additional departure course clearances first placed it on a south-southwesterly heading and finally on a pure-westerly one.
First Officer Feller audibly stated that he believed that they could quickly pass over the storm area and therefore avoid most of its effects, provided that they received further climb clearance. But, despite a request to Departure Control, they did not. The ominous storm now lay directly ahead. Avoidance could only be achieved by means of an immediate bank, but Feller’s request to do so, either to a southwesterly or southeasterly heading, was not granted because of traffic saturation.
As Departure Control feverishly searched for an available hole in the sky at a higher altitude, the silver and red quad-jet continued to barrel toward the storm’s core. Although clearance to bank and climb was ultimately given, the 720B only avoided a direct plunge through it, but was not spared its effects, now gripped by unrelenting turbulence. Left only with the choice of potential destruction if a banking maneuver were not initiated, it rode it out.
Now passing through 10,000 feet, Flight 705 was handed off to the Miami Air Route Traffic Control Center on a frequency of 118.9, but intercepting static made the transmission unintelligible. Forced to remain on the Departure Control frequency, it ascended through 16,000 feet and banked onto a north-northwesterly heading, at which point it was given a new ATC frequency. This, in the event, only proved briefly successful, because the weather at the 17,500-foot level through which it passed was so severe, that static-skewed communication was impossible. The air route traffic control center only heard two words from the aircraft, which either sounded like “number two” or “tank two.” They ended up being the last. The aircraft was at 19,000 feet. The time was 1:19 p.m.
Now slightly above this altitude, the 200,000-pound airplane was being tossed about like a scrap of paper by severe up-and downdrafts. The cockpit crew tried to regain control, but this was nothing more than an exercise in futility. Twelve seconds later it exploded, lighting the mighty black mountain formations from which it just emerged.
Like a fireball, it dove toward the Everglades, producing a volcanic eruption down to the annals of the swamp as it impacted, taking 43 lives with it 43 miles southwest of Miami International Airport.
A Coast Guard helicopter subsequently located the burning wreckage, which littered a ten-square-mile area, ten miles north of the Everglades’ Shark River.
The Boeing 720-051B was subsequently reassembled on wooden frames in an Opa Locka Florida hangar. The reconstruction, which encompassed 99 percent of the original airframe, proved to be the most extensive and costly project of its kind in Civil Aeronautics Board history and enabled investigators to determine that the aircraft’s wings had been subjected to a downward-caused negative force equivalent to 3.1 G’s, or one that was beyond design limitations.
According to the flight data recorder, the 720 had been climbing at an incredible 8,300- feet-per-minute at the time because of an updraft. The cockpit crew, as per procedure, trimmed the quad-jet to counteract this profile, but did not expect its severity. The downdraft that immediately followed created a nose-down tendency, ultimately inducing a dive and, with increasing speed, it became impossible to recover from it, leading to excessive, design-exceeding forces and inflight breakup.
The CAB did not issue its final report until June 4, 1965 because of the lengthy and extensive accident investigation, which revealed vital information about pure-jet airliner flying characteristics. It was determined that the crew had indeed attempted to counteract the aircraft’s downward pitch during its dive with a proper elevator deflection. But the flight surfaces had become ineffective in the midst of the tremendous forces to which they were subjected.
Structural failure began at the engine pylons, progressed to the 35-degree swept wings, and ended at its ruptured fuel tanks, whose ignition sparked the airborne explosion. Reduced to the equivalent of a limbless torpedo, it dove groundward and impacted with the Everglades.
The crash entailed the concept of turbulence upset, which was defined as vacillating up- and downdrafts, and their handling in pure-jet aircraft necessitated different flight surface deployments than those standardly used on piston and turboprop airliners.
In its final report, the Civil Aeronautics Board stated that “The Board determines that the probable cause of this accident was unfavorable interaction of severe vertical air drafts and large longitudinal control displacements resulting in a longitudinal upset’ from which a successful recovery was not made.”
Five months later, on July 12, 1963, history repeated itself when another Boeing 720, this time a series -022 operated by United Airlines, encountered identical weather conditions. Piloted by Captain Lynden Duescher, 42, First Officer Eric Anderson, 34, and Second Officer Ervin Rochlits, 41, United Flight UA 746 departed San Francisco at 6:25 p.m. with three other crew members and 53 passengers aboard. It routinely proceeded to its assigned flight level of three-seven-zero, bound, like the Northwest Orient aircraft, for Chicago-O’Hare. A severe storm warning, effective until 8:00 p.m. local time, was forecast over O’Neill, Nebraska, one of the cities on its flight plan.
As soon as the aircraft crossed over the Nebraska state line, it encountered minor turbulence, but an attempt to avoid it was made when a request to climb to flight level four-one-zero was made and granted. This did little to ameliorate the situation, however, since the turbulence only intensified, leaving the first officer to disengage the autopilot and reduce the aircraft to its 250-knot turbulence penetration speed.
The further eastward the 720 cruised, the worst the conditions became. Trapped in a parcel of clear air turbulence enveloped by the jet stream, it was subjected to a downdraft, all while it was flying in a nose-up attitude that produced an airspeed decrease.
As had been done on the Northwest flight, the elevators were raised to counteract the pitch angle and the engines were spooled up to overcome the downward pressure. Yet the severity of the turbulence that battled the very corrective measures created moderate buffeting and bespoke pf a pending stall.
A northeastward course change did nothing to enable the quad-jet to escape the turbulent conditions. Whipped by forceful, socking wings, it was barely able to maintain 37,800 feet. Still in its nose-high attitude, it continued to be thrown about by tumultuous wind currents. Havoc, needless to say, reigned in the passenger cabin.
The crew made an emergency transmission to Denver Center, but it could only spit out two words–“Aircraft uncontrollable.”
Now at a 35-degree nose-down pitch and building up a speed of 400 knots, it was reduced to a virtual dive-bomber and its futilely extended speed brakes did nothing to arrest the earthward plunge. Amid deafening cockpit warnings, the aircraft reached its never-exceed speed of 480 knots. Its instruments were now unreadable.
Flight 746 passed through the sound barrier at 25,000 feet, emerging from the clouds through which it had bored a hole, at which point the crew was able to catch a glimpse of the pearl-resembling ground lights of O’Neill, Nebraska, for the first time and visually gauge their current altitude.
The control column was slowly pulled back and the throttles were advanced to enable the 720 to arrest its dive in denser air, but at the same time avoid potential structural failure because of excessively abrupt changes.
It gradually responded. Further column pressure eventually enabled it to level-off at 14,000 feet and a subsequent re-ascent to a 1,000-foot higher altitude profiled it for its continuation to Chicago, where it safely landed.
Despite the wrenching the airframe had been subjected to, no structural damage had been inflicted. Its absence and safe return were, unlike the Northwest crew’s actions, the result of their decision to wait until lower, denser air rendered their pitch-changing elevator deflections effective.
The United 720-022 was removed from service and thoroughly inspected, but was subsequently pronounced airworthy when no damage was uncovered. Nevertheless, the incident revealed vital information concerning clear air turbulence penetration and demonstrated the design integrity of the aircraft when remedial action was taken at lower, flight surface effective altitudes.
The second fatal Boeing 720 accident occurred on May 20, 1965, but did not entail weather. A Pakistan International Airways 720-040B registered AP-AMH, which had been delivered only five days earlier, departed Karachi on its inaugural flight to London with intermediate stops in Dhahran, Cairo, and Geneva under the command of Captain Akhtar Aly Khan, a 17-year veteran, along with twelve other crew members and 114 passengers on board.
An approach to Cairo, after a routine intermediate landing in Dhahran, resulted in a mayday call, during which the captain reported engine difficulty and an undercarriage fire. Only five minutes from touchdown, it careened into the sand hills of the Suez Desert at 2:00 a.m., bouncing twice, and exploding, which lit up the night with a blazing conflagration.
Because of the crash site’s inaccessibility, it took six hours for the first of the United Arab Republic Air Force’s helicopters to reach it. Of the 127 on board, only six passengers were found alive, along with an equal number of baboons that had been carried as live cargo in the lower deck holds. It was the worst accident in PIA’s history at the time.
As a classic controlled flight into terrain, the accident’s probable cause stated as its inability to maintain adequate height for the circuit and its continued descent until it contacted the ground. The reason for that abnormal continuation was not determined.