Leak in a passenger aircraft ? - Decompression | Hypoxia


28 Jun 2021

Unfortunate decompression at 24000 feet

A freezing wind of hurricane force is roaring through the cabin. There's not enough oxygen onboard. The flight declares an emergency yet nobody can hear you. Sounds like a nightmare? Unfortunately, for everyone onboard Aloha Airlines Flight 243, it was a reality.

On April 28, 1988 , Aloha Airlines flight 243, scheduled to fly between Hilu and Honolulu in Hawaii, sustained extensive damage during flight. Though the aircraft was able to divert safely at the nearby Kahului airport in Maui, 65 passengers including the crew were injured, not to mention a flight attendant at the time was also ejected out of the aircraft. This incident consequently, had far-reaching effects on aviation safety policies.

Aloha Airlines Flight 243

So, what exactly caused the emergency that injured many and led to the ejection of a crew member at 24,000 feet ?

What is Aircraft decompression ?

The Aloha Airlines Flight 243 is a classic example of an aircraft depressurisation/decompression. Decompression in simple terms refers to the inability of the aircraft to maintain its designed pressure schedule. Failure to maintain this schedule can be attributed to a malfunction of the system or structural damage to the aircraft itself.

boldmethod - Time of useful consciousness

Why should aircrafts be depressurised, you may ask? As an aircraft gains altitude, the air becomes thinner and it gets difficult to breathe which is why it becomes imperative to mimic conditions similar to that at sea level. Typically modern aircrafts are designed to maintain a pressure of 14.7 PSI -which is generally found at sea level. Now this implies the air pressure inside the cabin is higher than the pressure outside and this pressure differential is maintained to protect the pilots, cabin crew and the passengers from Hypoxia- which is a state of reduced awareness due to insufficient supply of oxygen to the brain.

Types of decompression

Depending on the type of severity and the loss of pressure, it is predominantly divided into 3 categories:

Explosive Decompression : Any decompression which occurs rapidly, say less than 0.5 sec, is graded as explosive decompression-Exactly the one which occurred aboard the fateful Aloha Flight 243. This is one which is potentially fatal as it occurs faster than the lungs can decompress. The extreme noise in such an event can lead to utter confusion and distraction from flight duties, not to mention the danger of flying debris onboard.

Rapid Decompression : Almost similar to explosive decompression yet different in the fact that here the lungs can decompress faster than the cabin and hence the risk of lung damage is significantly less. One can experience  decrease in temperature, as the cabin temperature equalizes with the outside air temperature, Cloud of fog or mist in the cabin that is due to the drop in temperature, and the change of humidity.

Slow Decompression : Warning systems onboard generally notify the crew about depressurisation but it so happens that they do not always indicate the incidence of a slow decompression which can turn fatal only if undetected at early stages. One of the first physiological indications of a slow decompression may be eardiscomfort or ‘popping’, joint pain, or stomach pain due to gas expansion.

Blurred sight

Possible causes

It is to be noted that specific outflow valves maintain cabin altitude at the desired levels. A failure of the system that manages the valves can result in depressurisation. Irregular airflow , unserviceable components in the aircraft air-conditioning system or an engine malfunction can inhibit the free flow of fresh air. Now technically cabin doors are so designed such that the risk of depressurisation is next to nil even if the door is opened while in flight or intentionally. That said, improper maintenance of aircraft parts, fuselage, cracked windows, improper sealing of a door or a window can all lead to structural failure mid-flight , leading to a fatal decompression event.


The effects of hypoxia (lack of oxygen) cannot be over emphasized. It is important for the cabin crew to realize that even mild hypoxia, though not fatal, can have fatal results. This is because hypoxia can significantly reduce the crew member's ability to perform, and consequently lead to errors that may be fatal. The insidious nature of hypoxia causes a subtle decrease in individual performance, followed by incapacitation, the symptoms may not be identified until it is too late.

Hypoxia can cause a false sense of well-being. It is possible for a person to be hypoxic and not be aware of their condition. Therefore, it is important that the cabin crew recognizes the signs of hypoxia, and provides oxygen as soon as possible, in order to prevent a loss of consciousness.

Oxygen used by Pilots of Fighter aircrafts

Expected steps from the flight crew

The pilots are trained to immediately notify the ATC of the current issue. Normally in the event of depressurisation, pilots descend to a minimum safe altitude of 10,000 feet where the pressure outside and inside becomes more or less similar and it gets easier to breathe. However, the crew may initiate descent with/without obtaining clearance depending on the severity of the situation.

Following a decompression event, the crew is expected to execute the following:

Immediately grab the nearest oxygen mask and stay putSit down on the chair or secure oneself against any tight object.

“The amount of time for which the crew and passengers can perform their duties in an environment devoid of sufficient oxygen” – EFFECTIVE PERFORMANCE TIME

Incapacitated crew would only be a liability in assisting other crew members and passengers. In one such decompression event, a flight attended was heaved out of the cabin head-first but fortunately a passenger clanged onto her ankle that ultimately saved her. Hence personal safety of the cabin crew first cannot be stressed enough.

Cabin oxygen mask

Is this preventable ?

Though such incidents are rare, they do happen and when they do, the aftermath can be catastrophic. Hence to prevent such mishaps from occurring it becomes very important for the pilot and cabin crew to recognize the types of decompression and the immediate course of action that should be followed following such an event and limit the risk of hypoxia and ensure flight safety. The role of operators is equally important as regular recurrent training modes should be implemented emphasising the importance of effective communication (CRM). All it takes is just seconds for an incident to turn into an accident. And that can always be prevented.

At 20,000 Ft, Air India Flight To Frankfurt Suffers Cabin Decompression, returns back safely to Indira Gandhi International  - NDTV (6th March 2019)

IndiGo’s Lucknow-Bengaluru flight on Friday night landed safety at its destination after the aircraft suffered cabin depressurisation when it was about 240 km away from Bengaluru. The Airbus A320 (VT-ITM) has been grounded there for checks and the Directorate General of Civil Aviation is probing the snag. - Times of India (3rd April 2021)

Read next

DGCA warns airlines strictly against selling unusable seats to passengers

Radhika Bansal

25 May 2022

The Directorate General of Civil Aviation (DGCA) on Tuesday, May 24 warned airlines against offering unserviceable seats to passengers on their domestic and international flights.

Earlier this year, the DGCA had conducted an audit of seats and other cabin fittings in aircraft of airlines and found that many had broken or unserviceable seats.

In a communique sent to all Indian carriers, the DGCA said that some of the carriers are offering unserviceable seats to passengers on their scheduled international and domestic operations.

DGCA warns airlines strictly against selling unusable seats to passengers

"This practice is not only causing inconvenience to the travellers but also inviting a serious safety concern as well," the regulator said.

As per Rule 53 of The Aircraft Rule, 1937, all materials including the aircraft seat shall conform to approved design specifications. The installation of any part failing to meet the intended design requirements degrades the requirements of airworthiness, it said.

"Given the above, it is hereby advised to ensure that airlines shall not book passengers beyond the serviceable seats meeting the approved design specification available in the aircraft, released for scheduled services. Any non-compliance in this regard shall be viewed seriously," it noted.

A passenger booked on the flight (AI 161) said that business class passengers were downgraded due to the chaos, and some could not even fly as "their seats were not working."

On May 24th, passengers booked on a London-bound Air India flight from New Delhi were inconvenienced by several hours of delay and chaos over seat allocation on account of some seats not "working."

A passenger booked on the flight (AI 161) said that business class passengers were downgraded due to the chaos, and some could not even fly as "their seats were not working."

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Last month, the DGCA had asked Air India to repair its aircraft after a passenger complained of shabby interiors. The passenger had posted on social media a couple of pictures of shabby interiors including a broken armrest of Air India’s Airbus A320 aircraft.

ALSO READ - SpiceJet grounds its B737 aircraft after passenger complains about the cabin’s poor condition

DGCA had conducted an audit of seats and other cabin fittings in aircraft of airlines and found that many had broken or unserviceable seats.

In April, the DGCA had also grounded a SpiceJet aircraft over a passenger’s complaint of dirty seats and malfunctioning cabin panels. The SpiceJet plane took to the skies a day later after all the suggested repairs were effected.

The aviation regulator earlier in May warned aviation companies to follow the rules regarding passenger boarding or face penalties, after receiving multiple complaints of overbooking.

The DGCA in a statement said, "It has come to the notice of this office that various airlines are denying boarding to passengers holding confirmed tickets on a flight, although they have presented themselves for boarding within the time specified by the airline. This practice is extremely unfair to the passengers and brings a bad name to the aviation industry."

The aviation regulator earlier in May warned aviation companies to follow the rules regarding passenger boarding or face penalties

The aviation companies overbook to make sure most of the seats are sold just before the flight takes off. The airline has to face losses due to cancellations and the passengers not turning up, so they started overbooking the flights to make up for the loss.

However, if all the passengers do arrive, some have to be turned down resulting in denying boarding to passengers having a valid ticket and have arrived on time.  

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