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On November 22, 2020, passengers onboard a FlySafair Boeing 737-400 were left shaken when cabin pressure failed, leaving three of them bleeding from the nose, five with severe ear pain, and one in need of medical attention.

The plane was forced to make an emergency landing in George.

Perhaps “shaken” is too tame a word.

An investigation launched into the incident by the Civil Aviation Authority has concluded, providing answers as to what happened to cause the carnage.

The Civil Aviation Authority’s (CAA) report states that the Boeing 737-400 with registration ZS-OAF left Cape Town International Airport on time and en route to East London.

While the plane was climbing through 32 920 feet above mean sea level to a cruising altitude of 33 000 feet, the crew broadcast a “Cabin Altitude Warning followed by a Mayday, requesting emergency descent”.

Things got so bad aboard the flight that the pilots put on their oxygen masks, but “oxygen masks were not deployed in the cabin area”.

The aircraft commenced a descent to 10 000 feet. Once the flight was levelled off the plane diverged to George Airport where it landed safely on runway 29.

Before the flight took off, a senior cabin crew member informed the pilot-in-command that two of the doors weren’t closing properly. They were disarmed and closed again three times with a technician watching from the outside before they stayed shut.

Three times.

After take-off, “the crew had no lateral navigation and vertical navigation”. In addition to this, “the throttle hold stayed on after take-off, and the autothrottle was disconnected manually”.

For the remainder of the flight, there was no autothrottle available.

TimesLIVE reports that the traffic collision avoidance system on the aircraft, which reduces the risk of midair collisions was also inoperative during the flight.

And “during the initial stages of the [emergency descent to about 3km], the thrust levers retarded to low idle”, setting off cockpit alarms including one that warned the pilots the aircraft’s speed was too low.

Image: The low idle warning light in the cockpit of a Boeing 737-400, Civil Aviation Authority

The website b737.org.uk, which contains contributions from pilots and engineers worldwide, says: “The minimum engine speed for all flight phases is high idle, which varies with flight conditions.”

The emergency descent and loss of cabin pressure ultimately came down to damage to an air duct in the plane:

Image: Civil Aviation Authority

The plane in question, which appears to have its fair share of troubles before it took off, was manufactured in 1991 and had logged 65 823 hours (equivalent to 7½ years) in the air.

Its last safety inspection before the flight took place on October 27, and its airworthiness certificate was due to expire on April 30, 2021.

[sources:caa&timeslive]