The loss of cabin pressure on Jet Airways flight 9W 697 early on Thursday morning would have been, from initial reports, a terrifying experience for passengers on the Boeing 737 aircraft as dozens experienced bleeding from the nose and ears.
Initial reports attributed the Jet Airways episode to the crew forgetting to switch on the 'bleed' air switch, which allows the flow of air from the engines to the cockpit after it is cooled. However, the sudden drop in cabin pressure and the fact that passengers started experiencing bleeding, paradoxically, may just have ensured the Jet Airways crew were alerted to the problem and could return to Mumbai.
The Jet Airways incident draws attention to the often-ignored, and misunderstood, dangers posed by cabin pressure issues and brings back memories of the crash in Greece of a 'ghost' aircraft owned by a Cypriot budget airline in 2005.
The crash of Helios Airways flight 522 from Larnaca, Cyprus, to Athens in 2005, which left 121 people dead, made international headlines given the mysterious circumstances under which it occurred. The aircraft was tracked as being on radar for more than two hours after the pilots stopped responding to ATC messages.
When the Greek military scrambled fighter jets to intercept the non-responsive Helios aircraft, the pilots noticed oxygen masks dangling inside the aircraft, which eventually ran out of fuel and crashed near Athens. The fighter pilots also noticed two people with portable oxygen masks moving to the cockpit.
There were concerns that the Helios crash, also involving a Boeing 737, may have been linked to terrorism. However, investigations revealed that the aircraft had suffered a 'gradual' loss of cabin pressure, which was distinct from the episode on the Jet Airways flight on Thursday.
The Helios flight tragedy was blamed on the maintenance crew setting the aircraft's pressurisation switch to a 'manual' setting, instead of the mandated 'auto' setting, which would ensure that the cabin pressure would be adjusted to ensure optimum oxygen supply.
If a sudden loss in cabin pressure typically leads to dizziness, headaches and nose bleeds, a gradual loss in cabin pressure has a more insidious impact as it leaves no visible physiological symptoms while affecting the brain.
The onset of 'hypoxia' (oxygen deprivation) adversely affects brain functioning, preventing an individual from undertaking even simple tasks, such as understanding questions and commands such as being told to put on an oxygen mask right in front of him.
By the time, Helios flight 522 crashed, investigators believed all the crew and passengers would have been unconscious on account of the low air pressure. It later emerged the two people seen in the cockpit were cabin crew members, one of whom was a trained pilot, who were trying to save the aircraft. However, by then, the aircraft had run out of fuel and crashed.
The pilots of the Helios aircraft were found to be at fault for not spotting the changed setting on its pressurisation system during preflight checks. Helios Airways faced investigations in Cyprus and Greece, which found a number of violations in maintenance procedures. Helios stopped operations in 2006 after its bank accounts were frozen.
While the Jet Airways and Helios Airways incidents were different, both highlight the grave danger posed by overlooking routine procedures ... Such as flipping a switch.
