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Ask anyone which airliner first broke the sound barrier and they will say Concorde. They will be wrong by seven years — and by one very ordinary-looking Douglas jetliner that most people have completely forgotten.

On 21 August 1961, a standard Douglas DC-8 — the same four-engine airliner that carried holidaymakers across the Atlantic — was deliberately pushed past Mach 1 in a screaming dive over the California desert. It remains the only conventional airliner ever to go supersonic on purpose, other than Concorde and the Soviet Tu-144.

A test, not a stunt

The flight had a serious purpose. Douglas wanted flight-test data on a new wing leading-edge design, and pushing the DC-8 to its limits was the way to get it. But there was showmanship in it too: Magruder wanted to prove his airliner could survive Mach 1 — and grab some publicity from arch-rival Boeing’s 707.

The plan was audacious. Take a brand-new airliner up to above 50,000 feet — itself a record altitude for a commercial transport — then roll it over into a dive and let gravity do the rest. Chase planes came along to film it: an F-100 Super Sabre and an F-104 Starfighter, the F-104 reportedly flown by Chuck Yeager.

Sixteen seconds — and a scare

As the DC-8 plunged, the Mach needle crept past 1.0 and held there for about 16 seconds. Flight-test engineer Richard Edwards, aboard the aircraft, remembered the moment vividly decades later.

Scary is the right word. In the dive the elevators lost their bite and the stabilizer motor stalled against the enormous aerodynamic load — for a few seconds the airliner did not want to pull out. Magruder’s solution was pure test-pilot nerve: he pushed further into the dive to unload the tailplane, which restored control and let him haul the DC-8 level. Throughout, his manner was famously unflappable.

The flight data put the peak, Mach 1.012, at 41,088 feet; Edwards’ “about 45,000 feet” is his later recollection. Three months later, N9604Z was delivered to Canadian Pacific Air Lines on 15 November 1961, re-registered CF-CPG and named Empress of Montreal. It spent the next two decades doing exactly what every other DC-8 did, carrying passengers, later as CP Air’s Empress of Buenos Aires, before being scrapped at Opa-locka, Florida, in May 1981. Its supersonic record stood until the Tu-144 flew in 1969.

No airline ever built a business on supersonic DC-8s, of course. But the next time someone tells you Concorde was the first airliner through the sound barrier, you can gently correct them — and tell them about the day an ordinary jetliner went looking for Mach 1, and found it.

Sources: Smithsonian Air & Space Magazine; HistoryNet; This Day in Aviation.