How can this possibly occur?
I had to really think about this one before answering. The 737 is still being operated like it was in the 60s. It is a very ‘manual’ aircraft. The article says that the crew “failed to flip the bleed switch". The aircraft can actually be dispatched with both engine bleeds off but the APU bleed must be on. This is not a normal configuration.
Without getting into too much detail: If both the aircon packs were off, aircraft is unpressurised. Even if only one was one off it could still operate at FL250. At 6:30am it was already about 30°c. With the packs off, if would have been noticeably hot and stuffy both in the cabin and flight deck. An indicator that there’s no airflow.
The last thing being the actual pressurisation mode selector was selected to manual (think Helios).
Surely there must've been multiple warnings about the failure of the plane to attain the required pressure inside the cabin?
There may have been a master caution after start up (will check) but definitely an altitude horn at 10,000ft. This is consistent with the FR24 data that shows it got to 11,000ft before making a descent back to 10,000. Automatic activation of the oxy masks is 14,000ft so the crew manually activated the masks.
How many items on the checklist relate to this important safety item?
As I said above the 737 is a ‘manual’ aeroplane. The FO on the ground has the job of covering the entire overhead panel, MCP, their side or EFIS controls and the centre pedestal. In a preflight scan, I check to make sure every switch is where it needs to be. The preflight checklist, checks the pressurisation mode control in AUTO.
The next time the checklist picks it up is in the after take off checklist, ENG bleeds and both packs in AUTO. Both pilots usually check this and I’ll also add the check to the cabin rate to see if it’s pressurising. Then that is it. At 10,000ft I’ll do a last check of the pressurisation (my last chance to capture it) but there’s no checklist and no mention of it.
