B737 - catching a Pressurisation problem during after takeoff checks

[Tee Emm]

Several years ago, Boeing changed the after take off checklist in the 737 Classics by deleting the first item which was Air Conditioning and Pressurisation... Check. It was replaced with:

Engine Bleeds....On
Packs...............Auto.

If I recall correctly (very long time since I flew a 737) Vol 1 in those days, amplified the earlier check list item by stating that as part of the Pressurisation part of the check, the crew verified Engine Bleeds on and Packs on and - critically - mentioned a check that the aircraft was indeed pressurising, by looking at the pressurisation instruments on the Cabin Altitude Panel. Now it may be that last bit was only published in the Boeing 737-200 FCOM and I am getting my series mixed up.

The current B737 Classic FCOM Vol 1 After take off amplified procedures states: After flap retraction is complete:
Set or verify that the engine bleeds and air conditioning packs are operating.

There is no mention at all to check the Cabin Altitude Panel for correct pressurisation taking place. The problem being that unless it is a specific checklist item, many pilots simply don't want to know about it. The old word Airmanship again comes to mind in these instances.

For what it's worth, this writer did a unofficial simulator study of over 50 sessions over a period of several months during B737 type rating training and recurrent checks, involving how crews conducted the after take off checklist.

About 90 percent of crews failed to include the Cabin Altitude instruments in the after take off scans. When faults were induced that meant the cabin altitude rate of operation was clearly displaying an inappropriate reading, or the cabin was not pressurising, crews did not pick this up until the Cabin Altitude Warning sounded at 10,000 ft cabin altitude. The "defect" could have been picked up much earlier during the after take off scan - providing the scan had been done as per Boeing recommendation once the flaps had been retracted.

Where the crew delay the after take off scan until later in the climb, either for operational reasons or published company procedures, then the delay in picking a defective pressurisation can compress trouble shooting action by the crew.

The original Boeing after take off scan and checklist item of "Air Conditioning and Pressurisation.....Set" covered things nicely, IMHO, as it forced the crew to check the Cabin Altitude Panel in order to pick up a problem much earlier in the climb.

Finally (again for what it is worth), during the unofficial study, it was noticed that the PF (whether the captain or F/O) very rarely verified by looking that the PM had indeed completed the after take off checklist correctly. Most of the time, the PF would later admit hearing the PM reading out the Challenge and Response items but the PF was too busy (or too lazy perhaps) to check if in fact the items were correctly completed. It was if the PF thought that the after take off scan and checklist reading was not his problem but the full responsibility of the PM.

It used to be a well established principle of checklist operation that one pilot reads (challenges) and the other pilot verbally responds. That principle of a double check by both pilots has since been replaced by the current situation in some checklists where the checklist reader states out aloud the item (challenge) and then answers his own challenge.

It could be argued this tends to leave the other pilot out of the loop so to speak? If the subject interests you, then comments are most welcome

[ezy0000]

Having previously flown the 737 I now fly a type that doesn't have an after take off checklist. One thing I took with me though is a visual check of pressurisation after the flaps are retracted. A silent check that I do myself. It's not an SOP but its definitely something I want to make myself aware of as I get further from the ground. I check it again passing 10000'.
I'd wage a few quid most pilots on type probably don't do that but there's probably other items they might run their eye over. Either way I too think its an item that should appear on a checklist with a "check it's working" rather than a "check the correct switches have been pushed" element.
Interesting you mention airmanship. Unfortunately I see a worrying trend of management wanting to narrow our scope to use it. Rather than let airmanship/common sense have a wider role to play, they prefer to stick another few lines into our ever-expanding operating manuals to try and mitigate seemingly obvious/avoidable obstacles in our operation. With each new manual update/checklist revision we see changes that lead to consternation. It's all rather frustrating.

[BARKINGMAD]

My personal check involves treating the cabin alt instrument like a clock.

It usually starts on the ground at "midday", unless you're operating out of high altitude fields.

If my "clock" is working correctly, then the minute hand always moves faster than the short one. Therefore, at after take-off checks time the clock reads 12.10 to 12.15.

At FL100 I check it again, should read 1225, at FL200 it reads 1235 and at FL300 I check for 1340ish.

Any other reading noted and I will start to take a deep and abiding interest in what's happening.

Totally NON SOP for any airline I worked for and the suggestion it could be used as a teaching aid to those new-to-type fell on deaf ears, not-invented-here syndrome.

I like to think it comes under that wonderful non-PC word "airmanship", long since written out of the books. My first airline's SOP was altimeter checks every 5,000 ft in climb and descent including cabin alt, but the new people running the asylum seem to have forgotten the old ways.

That airline had attempted to move mountains, twice, with the inevitable tragic results and it seems such an event or a "Helios" encounter is needed to improve SA in relation to both pressurisation problems and granite chipping.

I totally agree with the point about current checklist philosophy and can't understand why a traditional method of ensuring things were done, correctly, has been superseded by the latest fad in areas of responsibility and checkreader also doing the action.

Come the accident(s) presumably it will all revert to the previous way, meantime look after # 1, though not much good if you're SLF on someone elses 'craft

[Al Murdoch]

Unfortunately the main issue here is one of design. The 737's A/C and pressurisation ergonomics are simply awful. It is of no great surprise that there have been so many pressurisation incidents and accidents on the type, even the NG, due to Boeing's reluctance to install something that is easy to check in the very busy post-takeoff environment.
It's not all down to bad airmanship.

[Centaurus]

The 737's A/C and pressurisation ergonomics are simply awful. It is of no great surprise that there have been so many pressurisation incidents and accidents on the type, even the NG

Interesting viewpoint and I have read similar remarks from others. Having only ever flown the 737-200 and Classics and a few hours on the F28 Fellowship, I am not in a position to compare with other jet transports.

But I must say, I have never struck finger trouble with the 737's pressurisation systems despite many years on type. On the contrary, I found it simple to operate if you use a modicum of care as with any other systems on other types.

[BOAC]

With Centaurus. The 737 system is fine if things are done properly. If a 'read and don't do' lackadaisical approach to checks is allowed to develop it can bite. No surprises there, then, and perhaps a lesson to be learned.

I had always looked at cabin roc and altitude at 5000' intervals (same school as Barking) and in the cruise. Following the Helios accident I took to watching F/Os (as PM) do the after-take-off checks and for a few weeks not one of them was looking at these dials. Then they did...................

Out of interest, when I 're-trained' in BA sops in the 90's I was told "we only do checks in the climb every 10,000' and not above 20,000'" Some wag told me it was because the ATP never reached 30,000'..............:)

[latetonite]

BOAC, I include the pressurization in the after take off checks. Even when I am PF, I have a quick glance. At 10.000 ft again, the famous 10-4 on the pressure dial, however, by now the plane will check it for you if you left the packs off.
I just prefer to avoid the embarrassment. And yes, again every ten thousand.

[Jwscud]

At my company, the SOP during the after takeoff checks is to call out the cabin differential pressure during the after takeoff checks as you check it. So the call would be Air Cond and Press - 2.2 and set. It's also called aloud at 10,000 feet, then silently 20k, 30k (and 40k if you're going that crazy high).

The 12:10, 12:25 and so on method was also taught during type rating training for a rough approximation of where the needles should be. The other gotcha is the cabin RoC gauge - if you are doing a very short sector with a low cruise, the cabin may stay at 0 for the entire flight hence 0 diff press and zero RoC/RoD and this can incorrectly be interpreted as a pressurisation failure.

[aviatorhi]

Back when we had 3 man cockpits we used to use this thing called airmanship. :ok:

[Tinstaafl]

Beancounters have decided it's better to have more 'ship' than 'man'.

[CallmeJB]

if you are doing a very short sector with a low cruise, the cabin may stay at 0 for the entire flight hence 0 diff press and zero RoC/RoD and this can incorrectly be interpreted as a pressurisation failure.


Correction: RoC/RoD will stay at zero, the cabin altitude will stay at 0 (if you're landing at 0), but the diff press will increase as you climb and decrease when you descend.

[DozyWannabe]

I like to think it comes under that wonderful non-PC word "airmanship", long since written out of the books.

Small point of order in grammatical terms - there's nothing PC or otherwise about the term "airmanship" because there is no political dimension to the term (except arguably being gender-specific, but we're splitting hairs). The term may have fallen out of use in ground school, but the skillset is still very much appreciated.

[RAT 5]

After flap retraction is complete:
Set or verify that the engine bleeds and air conditioning packs are operating.

There is no mention at all to check the Cabin Altitude Panel for correct pressurisation taking place.

Am I being simple here and missing something? The Bleed switches and Pack switches can be on, BUT to verify that "correct pressurisation is taking place" means checking that the diff' is rising, the cabin altitude is still low and the cabin ROC is acceptable, probably zero.
Please don't say we have reached the day of nobody doing sensible things unless led by the nose.
Sadly I have seen that to be true. Airmanship is not encouraged. SOP's rule the roost. Too often a suggestion of 'how about doing this or that for good measure....' was met with a "where is that written?"