Pressurized Flight Cabins and the Japan Air Lines....

Why flight cabins pressure has to be maintained when it is at air...?

Wikipedia has a pretty comprehensive article on this subject and with that here I am telling you a disaster happened due to a carelessness.

But the short answer is that even at 8,000 feet (the altitude at which most airliners are pressurized) there is 25% less oxygen in air than at sea level. Most people in good health can cope with that.

However, by the time you get to 35,000 ft - minimum cruising altitude for most commercial flights - the amount of oxygen in the air is around 75% lower than at sea level. With this amount of oxygen in the air most people will be unconscious within seconds and dead not too long after that.

Even at lower altitudes there are effects which is one of the reasons Boeing have made much of the 6000 feet altitude at which the 787 Dreamliner is pressurized. This brings the oxygen content to around 20% lower than it would be at sea level.

You are probably aware that if cabin pressurization fails oxygen masks will come down. These will supply sufficient oxygen to keep everyone safe until the pilots can get the plane below 10,000 feet - which they will do pretty rapidly since there is only enough oxygen in passenger masks to last around 15 minutes. For this reason planes do not fly over terrain that would prevent them dropping to a safe altitude.

One careless mistake by a Boeing engineer which resulted in 520 deaths, resignation of Japan Airlines then President, suicide of one of the guilt-stricken maintenance managers of Japan Airlines and about one-third drop in air travelling in Japan.

The Event?

Crash of japan Airlines Flight 123

What happened?

This is called rear pressure bulkhead which is located between the cabin and the tail of the aircraft. It is a vital part of the plane which seals the rear of the plane and thus maintains cabin pressure.

In 1985, Japan Airlines Flight 12 crashed after the rear pressure bulkhead failed due to a faulty repair after a tail strike seven years earlier, when a single repair patch plate was incorrectly cut in two "to make it fit".

Boeing later calculated that the incorrect installation would be expected to fail after approximately 10,000 pressurizations; the repaired aircraft accomplished 12,318 successful flights before the crash.

Aftermaths?

• Only 4 survivors, 520 died
• Delayed rescue operations resulted in more fatalities
• Domestic flight travel in Japan reduced by 25-30 % after this incident
• Then President of Japan Airlines resigned
• One of the maintenance managers of JAL committed suicide
• Japan Airlines never used flight number 123 again

How the Pilot and the crew tried their best till the end to save the plane is another great story. They managed to keep the plane in air for more than 30 minutes before finally giving up which is a record in itself and National Geography channel made a documentary film on this.