Passengers aboard easyJet flight 8275 from Gatwick to Madrid on Wednesday encountered two surprises. The first: they were kept waiting on the ground for nearly two hours because of a strike by French air-traffic controllers. The second: all six crew members on the Airbus A320 were women.

The arithmetic shows this to be a rare event. While many cabin crew are female, men outnumber women by around 16 to one on the flight deck.

When I checked on the flight-deck gender split three months ago with all the leading airlines serving UK passengers, a remarkably consistent pattern emerged: at British Airways, easyJet, Monarch and Ryanair, just 6 per cent of crew are female.

Flybe performs slightly better than the norm; 7.5 per cent of the airline’s pilots are female, while just 3 per cent of Thomson’s pilots are women.

All other things being equal, only one flight in about 300 to and from the UK is flown by two women; 17 have have one male and one female pilot; and the remaining 282 are two-man operations.

But not all other things are equal, because the proportion of captains who are female is even smaller than that 6 per cent. At Thomas Cook Airlines, for example, 8 per cent of first officers – junior pilots – are female, but among captains, the proportion of women falls to below 2 per cent.

Worldwide, the figures are even worse, with only 3 per cent of pilots worldwide female – raising the odds of a two-woman flight crew to a shocking one in 1,000.

Pilots were warned about the French strike by a Notam – a NOtice To AirMen, which most of the time is well aimed.

Royal Brunei's all-female flight deck made headlines last year (Royal Brunei Airlines)

As the captain of that easyJet flight said, “It is hard to think of another high-profile profession where women are so under-represented.” She is Kate McWilliams, at 27 years old also the world’s youngest female commercial captain.

The flight on International Women’s Day was more than just a gesture: easyJet has set an ambitious target of increasing the proportion of its female pilots, aiming for 20 per cent of new-intake pilots by 2020. The airline has named an Airbus A320 jet after the pioneering female aviator, Amy Johnson, and that was the aircraft used for the pioneering Gatwick-Madrid flight.

It wasn’t the first time an airline has highlighted the high-altitude gender gap; a year ago, Royal Brunei Airlines operated its first all-female-pilot service, with a twist of irony to Saudi Arabia – where conservative clerics ban women from driving.

Given the hostile attitude to homosexuality in the Sultanate, I fear we may be waiting rather longer for the Bruneian carrier to dispatch a flight with openly gay pilots.

Across at easyJet’s giant rival, Ryanair, one female pilot has become an online celebrity as well as a role model: Maria Pettersson, from Gothenburg, combines her work as a first officer with a travel and lifestyle blog.

Talking of lifestyle: could one reason for the gender imbalance be the uncertain and disruptive schedule that pilots have to handle? I don’t believe so, because there are plenty of female cabin crew who cope with equally onerous rosters.

Civil Aviation Authority flight-deck rules that apply only to women pilots don’t help. Pregnant women can fly as a passenger on easyJet up to the 35th week of gestation, but under CAA regulations the limit is 26 weeks. “After this point, the certificate shall be suspended,” instructs the authority, adding a provision that makes having a baby sound like an affliction: “The suspension shall be lifted after full recovery following the end of the pregnancy.”

To see how the rails compare with the skies, I asked Eurostar how many of its train drivers are female. Just two out of 62, which means that men outnumber women by 30 to one.