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Home > Air Crash > Could the Helios Crash have been prevented easily?
Could the Helios Crash have been prevented easily?
Aviation - Air Crash
Tuesday, 09 December 2008 13:09

Dear Captain Lim,

I was fortunate to come across your website by accident while searching for another, after which I have been a frequent visitor reading articles on various topics related to aviation.
I happened to see a television program on the Air Crash Investigation of HELIOS B737 disaster. As far as I could understand, before the pressurization test during maintenance, the automatic cabin pressurization switch was switched from AUTO to MANUAL. It was not restored back to AUTO and caused the oxygen in the aircraft to decrease to a dangerously low level during flight. It left the crew and passengers unconscious.

In spite of the alarm at the cockpit and the communication to the ground maintenance officials, the pilots could not identify the problem.
Was this failure to identify and rectify the problem when the alarm came on due to improper training of the pilots or was it due to disorientation, panic or stress on the pilots?
What state of mind were the pilots in? How do you describe the situation?

I feel the situation could have been brought back to normal easily.

Wishing you a pleasant and safe flight


Helios Full Crash Investigation Part 1

Hi Sebastian,

It is easy for me to look from hindsight and say what could have been done right by the pilots to prevent that disaster.

Nevertheless, since you mentioned that, I will examine this with the notes from an ex-United Airline Captain (Robert J. Boser from AirlinesSafety.com) and see how the situation could have been brought back to normal easily.

The NTSB (National Transportation Safety Board) had determined that the probable cause of the accident was due to incapacitation of the flight crewmembers as a result of their failure to receive supplemental oxygen following a loss of cabin pressurization.

Capt Boser has lamented in his website that pilots do not always use oxygen when leaving the cockpit seat as required by the regulations.  The Regulations state that, "if for any reason at any time it is necessary for one pilot to leave his station at the controls of the airplane when operating at flight altitudes above flight level 250, the remaining pilot at the controls shall put on and use his oxygen mask until the other pilot has returned to his duty station."

When the cabin suddenly decompresses (for whatever reasons) at flight altitudes above 35,000 ft., the period of useful consciousness without supplemental oxygen, can be measured in seconds.  That is why both pilots have to have "quick don" oxygen masks at the ready, which will enable them to put them on and begin breathing pure oxygen in a matter of seconds, should such an emergency occur.  It is also why one pilot must don and use the mask, whenever the other pilot finds it necessary to leave his seat, if the plane is flying 25,000 ft. above sea level.

How could the pilots recover from this dire position easily?

Well, if only they had identified that they had lost pressurization, the immediate responses of the pilots should be to:

  • Put on the oxygen masks immediately; ensure that the switch is in the 100% position
  • Retard the thrust levers to idle
  • Disengage the autopilot on some planes or leave it engaged on others (depends on the cockpit design of that particular plane.) 
  • Extend the spoilers (panels on top of the wing, which act as speed brakes, when they are fully deployed).
  • Descend at maximum operating speed (this is popularly referred to as a "high dive" maneuver).
  • Select emergency transponder code to "ON" (to alert the ATC)
  • Ensure both oxygen mike switches are in the "ON" position, so the pilots can communicate with ATC and with each other.
  • Announce to cabin attendants and passengers, when time permits, that they should don their own oxygen masks. (On modern planes, this is done automatically)
  • Level the plane off at 10,000 feet, or higher if required by area terrain.

If these emergency procedures were followed, then the plane could lose all its cabin pressurization and still land safely.  Yes, this is what all pilots have been trained to do but why was this not done?

The investigation board found, amongst others, that the crew:-

  • Was unaware that the cabin pressurization mode selector was in the "MAN" (manual) position when it should have been in "AUTO" position.
  • Were confused over the warnings and the reasons for the activation of the warnings and therefore were not aware of the rapid loss of pressurization
  • Did not apply adequate Crew Resource Management (CRM) principles that resulted in the accident.

To other readers - for more information, please view this YouTube video "Helios Crash Full Investigation"


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