Breaking the sound barrier profitably is a notoriously tricky business. It's such a cool idea, being on an aeroplane that's flying faster than a bullet. Who wouldn't want to burn tens of millions of pounds, forge crazy foreign alliances and exhaust all of their political capital making that dream come true?
Plenty of aircraft exist that can do supersonic, but most of them achieve it by brute force alone. This isn't really an option for commercial aircraft, since they have to, you know, make money. Economic supersonic is an elusive creature, and some would argue that it has yet to be achieved. Perhaps incentives are what we're missing. Earth now sadly lacks an operational SST, and I don't care that I'd never be able to afford to fly in one—anyone who can claim responsibility for getting this beast into production deserves to have all of their empty things filled with cream for as long as they live.
So, moving on, this should be a very short list. In fact, to most people a list of airliners that have broken the speed of sound probably seems a bit of a no-brainer:
- Aérospatiale-BAC Concorde
No? Well, not quite. It's only fair to include both Evil Empires, in which case there's two:
- Aérospatiale-BAC Concorde
- Tupolev Tu-144
Not everyone knows this, or that the Soviet effort was faster (albeit somewhat crude and inefficient by comparison). You can make this slightly more interesting if you list them in chronological order of supersonic achievement:
- June 5, 1969 - Tupolev Tu-144
- October 1, 1969 - Aérospatiale-BAC Concorde
Yup. Although large parts of the Tu-144 design were ripped off from Concorde, it still achieved supersonic flight first.
Except that it didn't.
Here's the real chronological order of the first supersonic flights by passenger aircraft:
- August 21, 1961 - Douglas DC-8
- June 5, 1969 - Tupolev Tu-144
- October 1, 1969 - Aérospatiale-BAC Concorde
Wait, what? Isn't the DC-8 some geriatric narrowbody that was used by an intergalactic dictator for mass genocide 75 million years ago? That bucket of bolts broke the sound barrier?
It's true. Not only doesn't the supersonic roll call end with Concorde, it doesn't even start where you think it does. What the above aircraft have in common, though, is that when they went supersonic it was intentional. And two out of the three are designed for supersonic flight. Neither is true of the rest. These aircraft had what is sometimes called a supersonic excursion. I'll resist the really obvious abbreviation.
The following is a chronological list of flights by subsonic airliners that have or are suspected to have achieved supersonic flight. Although the speed of sound varies with altitude, air pressure and density, crucially air behaves in much the same way at specific proportions of the speed of sound, regardless of what that speed actually is (or: breaking the sound barrier in an aircraft not designed to do it is risky, whatever that speed is). At the typical airliner cruising altitude it hovers around 660mph. Your typical airliner's cruising speed is 500-580mph.
There are of course a number of other documented incidents of subsonic airliners going supersonic but they are omitted in the interest of good taste, for what should be obvious reasons. On we go.
Douglas DC-8 Test Flight
Over the testing range at Edwards Air Force Base, a four-engined Douglas DC-8 was put into a shallow dive from 52,090 feet (which incidentally was an altitude record for a passenger aircraft) at a speed of around mach 0.8 (80% of the 'local' speed of sound), followed by F-100 and F-104 chase planes to test the flight characteristics of a new wing design. By just over 41,000ft it had broken the sound barrier - the first time this had been done by a passenger aircraft.
A maximum speed of mach 1.012 was reached before test pilot Magruder attempted to pull out of the dive - and nothing happened:
The recovery was scheduled to start at 42,000 feet, however the initial application of full up elevator did not appear to produce any noticeable change in load factor. Also, with full up elevator applied, application of stabilizer trim appeared to indicate that the stabilizer trim would not function with the elevator in the nose up position.
It turns out that the supersonic shock wave that forms around an aircraft at that speed can have unusual effects on the controls of subsonic aircraft - effects from a simple reduction in control effectiveness to total inversion of flight controls have been recorded. That's part of the reason airliners don't fly faster than sound (that, and insufficient thrust to do it in level flight). Fortunately in this case a simple relax of elevator control with a bit of extra trim did the trick. Trim is an adjustable setting that causes a constant force to be applied to a control surface, like elevators, rudder or ailerons.
Interestingly enough the DC-8 was relatively stable while supersonic, and it was only while decelerating through mach 0.95 that there was any buffeting or other symptoms. There were no problems during the flight, and the aircraft landed undamaged.
Two days later Douglas Aircraft proudly put out a press release of the achievement, and sent out memorabilia that had been stowed on the flight to several VIPs afterwards: "this letter went faster than sound," etc.
|Date of incident:||August 21, 1961|
|Aircraft type:||Douglas DC-8-43; registration CF-CPG|
|Insanity rating:||5/10. Yes, this was a deliberate effort, but they deserve some insanity points for doing it in a passenger airliner in 1961.|
|Last seen:||unknown; aircraft |probably scrapped
TWA Flight 841 has actually had two incidents - in 1974 and 1979. The latter is decidedly less morbid.
During a flight from JFK International Airport to Minneapolis-Saint Paul International Airport, TWA 841, a Boeing 727, deployed one of its slats while cruising at 39,000 feet. This, as some of you will know, is very bad. Not many of you are likely to know why, however, so permit me to explain.
A slat is not a million miles away from a flap, literally and figuratively. A flap is a device on the trailing edge of a wing, which when deployed extends backwards from the wing and increases the lift that it generates at low speed. It is thus categorised as a high-lift device. The trade-off is that high-lift devices increase drag. A slat is another HLD, but is on the leading edge of the wing. It extends forwards when it is deployed, and allows the wing to continue generating lift at higher angles of attack, when it would normally stall. Again this is useful in low-speed situations like takeoff and landing.
However, if slats are deployed at cruising speed they can cause violent oscillations, and in this case only a single slat deployed on a single wing, which resulted the aircraft making a sharp roll to the right. The air loading the slat was subjected to made it impossible to retract and despite attempts at correction by the autopilot and the captain, the aircraft went into a spiral dive and lost over 30,000 feet during the next minute. As a comparison, I would estimate a typical high controlled descent rate for a passenger airliner to be 5,000 feet per minute or less. Analysis of the flight data recorder by the NTSB indicated that the 727 exceeded mach 1 during the dive, and it was only after the errant slat had been torn off and the captain deployed the landing gear for some extra drag that control was finally re-established at 5-8,000ft.
The aircraft was substantially damaged by the dive: the landing gear was damaged, parts of the flaps and the wing spoilers were missing and a raft of parts were missing or damaged, including a cracked cabin window. Despite that there were no further problems and once control was re-established, the crew made an emergency landing without incident. The investigation later concluded that there was no evidence of mechanical failure, and that the most likely cause of the incident was incorrect operation of the slats by the crew, which they strongly denied.
The 727 was repaired and returned to service later the same year.
This was a Boeing 747SP (a shorter, faster, baby jumbo jet) on a flight from Taipei to Los Angeles International Airport. Ten hours into the flight, about 300 nautical miles from destination while in cruise at 41,000 feet it flew through severe clear air turbulence. This resulted in a loss of power from number four engine (the outboard, starboard engine); despite the efforts of the flight engineer, engine four eventually flamed out.
Although the crew began procedures to relight the engine, they did it well above Boeing's recommended maximum altitude of 30,000 feet. A lack of rudder input meant the crew were not doing enough to correct the yaw caused by drag from the dead engine; although the autopilot was making corrective actions, the autopilot installed in 747s at the time only controlled the ailerons (which control roll, or bank) and not the rudder (which controls yaw). Both were needed to effectively counteract the extra drag, and in the absence of this the aircraft began gradually rolling to starboard.
The drag on the aircraft was also reducing its airspeed, and adjusting the autopilot for a shallow dive did not improve matters, so the captain disengaged the autopilot to increase airspeed manually. Unfortunately at the time the autopilot was applying maximum port aileron to counteract the drag from the dead starboard engine; the crew should have matched this with their manual controls when disengaging the autopilot but didn't, so the roll continued at a higher rate. The NTSB said in its report that the captain was focused almost exclusively on the airspeed problems at this point, and the aircraft was in cloud so there were no visual references to what the aircraft was doing.
After about 30 seconds the aircraft made a wing-over and rolled completely, descending rapidly at up to 60° down-angle and losing about 30,000 feet in less than two minutes. Speeds exceeded the airframe's maximum mach number of 0.92 (92% of the speed of sound) on two occasions, and strong gee forces were felt for several minutes, up to a maximum of about five gees. About ten feet of the port tailplane and five feet of the starboard, including large parts of the elevators, were ripped off by aerodynamic forces during the descent, and during the periods of high gee the inboard main landing gear was forced down which also resulted in several of the landing gear doors falling off. There was sundry other damage to the empennage area and the landing gear bays.
At 11,000 feet the aircraft broke through the clouds allowing the captain to get visual references, and finally stabilise at about 8,500 feet, after which engine four was successfully relit. With part of the landing gear down and one of the hydraulic systems empty, it was impossible to reach LAX with the increased drag, so the captain diverted to San Francisco International Airport and made an emergency landing. There were several injuries caused by the high-gee portion of the incident but no fatalities.
The NTSB concluded that the incident was caused by "the captain's preoccupation with an inflight malfunction and his failure to monitor properly the airplane's flight instruments which resulted in his losing control of the airplane."
Although the 747 was severely damaged by the incident—including the wings being permanently bent upwards—it was repaired and returned to service.