Arguably, the most important part of flying a commercial airliner is safely reaching the destination runway. While it sounds like an extremely straightforward task, a small procedural or technical error can lead to a huge problem — potentially including a multi-engine plane crashing into the ground. details how one small error nearly led to a plane crashing into the ground at Paris’s Charles de Gaulle Airport this spring, with pilots avoiding disaster by as little as six feet.

An Airbus A320 operated by Airhub Airlines, a Maltese charter carrier, nearly crashed on approach to Charles de Gaulle in late May. The Airhub flight departed Stockholm, Sweden at 9:30 am on May 23rd with a captain, co-pilot, four cabin crew and 172 passengers onboard. The flight nearly didn’t arrive due to an unfortunate series of events sparked by an air traffic controller reading out one incorrect digit in a four-digit number. , France’s civil aviation accident investigation agency, details what’s believed to have taken place.

The report states:

At 11:32:24, on approach to CDG, the Intermediate (ITM) controller instructed the flight crew to descend to 6,000 ft with an incorrect QNH (1011 instead of 1001 valid at the time),

“Red Nose 4 3 1 1, descend … descend 6,000 ft, 1 0 1 1.”

“The PM (Co-pilot) read back with this QNH, “6,000 ft, 1 0 1 1 … 1 … 0 1 1, Red Nose 4 3 1 1.”

QNH is an atmospheric pressure sub-setting for a plane’s altimeter, used to help determine the plane’s altitude relative to sea level. An incorrect setting would cause the plane’s instruments to display an inaccurate altitude. The incorrect digit in this case meant the AirHub A320's instruments displayed an altitude reading roughly 270 feet higher than the plane was flying.

It should also be noted that the A320 was in cloud cover for most of the approach, so the crew had no visual references through the plane’s windshield, and the airport tower controllers couldn’t see the aircraft.

With the aircraft’s descent profile and incorrect altitude, the Airbus A320 was on track to land a mile short of the runway. The plane’s Minimum Safe Altitude Warning (MSAW) triggered twice during the approach, but alarmingly, the Terrain Awareness and Warning System (TAWS) never activated. According to the radio-altimeter, the aircraft came within six feet of the ground before the captain decided to pull up and attempt a second approach. Yes, six feet.

Thankfully, the flight crew was able to establish visual contact with the runway to correct their descent profile on the second approach. The A320 made a safe landing without incident. The investigation is still ongoing and is expected to look into a number of questions, including why TAWS didn’t activate.