Centaurus
16th Oct 2005, 02:48
The Tech Log posts on the Helios B737 accident have covered so many pages that many interesting technical issues have been in danger of vanishing in a sea of argument and counter-argument.
There were two links in particular, that attracted my attention. Both were official reports on 737's that had climbed unpressurised after take off because through sloppy cockpit checks no one had noticed the packs were off.
The first officer ( his total flying experience was about 370 hours) in one of the incidents had covered the bleeds off procedure in his type rating course on the simulator, but had never seen a bleeds off procedure in the real aircraft.
Subsequently, when he was asked by the captain to reconfigure to bleeds on as part of the after take off procedure, he inadvertently turned both air-conditioning packs off. He then missed the error as he read the checklist and responded to his own challenge. The captain, busy on other matters, failed to double check that the new first officer had done his job properly.
Now I am not knocking the poor first officer - heaven knows I have seen the same confusion on re-configuring the switches on countless occasions, both in the real aircraft and in the simulator. In fact I have no doubt readers of this post will mutter "Been there - Done that" under their breath.
The weak link here is the design of the after take off check list where the first officer (or PNF whichever) having in theory conducted the required scans, then pulls out the checklist and reads and responds to his own actions. The captain hears his response and most times, without double checking, assumes that the checks are done.
With this accent on Areas of Responsibility so beloved of modern checklist philosophy, I have little doubt that errors of ommission such as described are common-place. Personally I prefer the old policy of one pilot reads and the other responds for all situations. After all lots of trees met their end in the writing of books and articles on how challenge and Response check lists are Good Things.
As a firm believer in Murphy's Law, I have long since learned in aviation one should never totally trust the pilot in the other seat even if he is your best mate. Always quietly and subtly double check that he has done his job because although a verbal response may be according to company SOP, his action may not have been. Do I hear more mutterings of "Been there - Seen that?"
Having got that little bit of bulsh..t off my chest, I would like to ask a question of the Boeing 737 technical experts reading this post.
In both the links referred to earlier, the air-conditioning packs were either inadvertently left off after engine start or switched off as part of re-configuring after take off.
Either way, the aircraft climbed unpressurised right from the word go. What has me tossed is in one case the cabin altitude warning sounded as the aircraft passed 10,000 ft unpressurised (as one one would expect). But in the second incident, the aircraft must have been partially pressurised because if I recall, the aircraft was around 20,000 ft when the cabin altitude warning sounded. In both cases the packs were off from take off yet the results were different.
In the 737-300 simulator that I flew, the aircraft maintained partial pressurisation in the climb to 20,000 ft with both packs off, and again, if I recall correctly, the cabin altitude did not reach 10,000 ft until the aircraft was around 20,000 ft.
Your comments would be appreciated.
There were two links in particular, that attracted my attention. Both were official reports on 737's that had climbed unpressurised after take off because through sloppy cockpit checks no one had noticed the packs were off.
The first officer ( his total flying experience was about 370 hours) in one of the incidents had covered the bleeds off procedure in his type rating course on the simulator, but had never seen a bleeds off procedure in the real aircraft.
Subsequently, when he was asked by the captain to reconfigure to bleeds on as part of the after take off procedure, he inadvertently turned both air-conditioning packs off. He then missed the error as he read the checklist and responded to his own challenge. The captain, busy on other matters, failed to double check that the new first officer had done his job properly.
Now I am not knocking the poor first officer - heaven knows I have seen the same confusion on re-configuring the switches on countless occasions, both in the real aircraft and in the simulator. In fact I have no doubt readers of this post will mutter "Been there - Done that" under their breath.
The weak link here is the design of the after take off check list where the first officer (or PNF whichever) having in theory conducted the required scans, then pulls out the checklist and reads and responds to his own actions. The captain hears his response and most times, without double checking, assumes that the checks are done.
With this accent on Areas of Responsibility so beloved of modern checklist philosophy, I have little doubt that errors of ommission such as described are common-place. Personally I prefer the old policy of one pilot reads and the other responds for all situations. After all lots of trees met their end in the writing of books and articles on how challenge and Response check lists are Good Things.
As a firm believer in Murphy's Law, I have long since learned in aviation one should never totally trust the pilot in the other seat even if he is your best mate. Always quietly and subtly double check that he has done his job because although a verbal response may be according to company SOP, his action may not have been. Do I hear more mutterings of "Been there - Seen that?"
Having got that little bit of bulsh..t off my chest, I would like to ask a question of the Boeing 737 technical experts reading this post.
In both the links referred to earlier, the air-conditioning packs were either inadvertently left off after engine start or switched off as part of re-configuring after take off.
Either way, the aircraft climbed unpressurised right from the word go. What has me tossed is in one case the cabin altitude warning sounded as the aircraft passed 10,000 ft unpressurised (as one one would expect). But in the second incident, the aircraft must have been partially pressurised because if I recall, the aircraft was around 20,000 ft when the cabin altitude warning sounded. In both cases the packs were off from take off yet the results were different.
In the 737-300 simulator that I flew, the aircraft maintained partial pressurisation in the climb to 20,000 ft with both packs off, and again, if I recall correctly, the cabin altitude did not reach 10,000 ft until the aircraft was around 20,000 ft.
Your comments would be appreciated.