B737. Why select bleeds off for Single Engine landing?

[Hudson]

The B737 Classic One Engine Inoperative Landing checklist includes a provision for additional go-around thrust if desired by configuring the pressurisation system for a no engine bleed landing.

The "If Desired" part raises a few questions in my mind and perhaps the experts can amplify this term.

I would have thought that at max landing weight for most conditions, the thrust available on the operative engine would have been well in excess of that required to achieve the minimum certified gradient of climb on one engine.

If not, I would have also thought that company performance engineers would have worked out the sums and nominated which specific airports would require the "additional thrust" to make the mimimum airworthiness or operational gradient in event of a go-around. High and hot airports for example?

Thus during the landing briefing, the route manual might require airport A as a bleeds off landing approach, while airport B does not. Currently with some operators, the decision whether or not to configure the bleeds is left to the discretion of the crew.

Similarly other operators require that all one-engine inoperative landings are configured for a no engine bleed approach - regardless of the landing weight.

It seems to me that the decision to configure or not when below max structural for landing is difficult to assess if one engine inoperative climb limit weights are not easily available in the cockpit - which normally they are not - unless one has access to a Flight Manual. Workload will normally prevent access to a Flight Manual.

So apart from a specific direction to configure bleeds off in the company route manual, how does the crew judge whether or not to configure to bleeds off in event of a one engine inoperative landing. Is it a case of when in doubt - configure bleeds off? Or is it a gut feeling to configure bleeds off? Seems a grey area to me.

[Bumblebee]

If carrying out a SE approach above max landing weight you'd use bleeds off - no question. Otherwise...how about when you have a terrain clearance emergency turn procedure to follow on the go-around...? Shouldn't be necessary otherwise should it, if everything else is within the published performance?:8

ps re your second last paragraph....aren't your airfield max landing weights and WAT limits in the company performance manual that you have on the flight deck? Or with whatever documentation you use to get your minima when you brief before top of descent?

[Blip]

The simple answer to your question is as Bumblebee has already mentioned. You may well be way above your MLW and need the extra performance.

Infact you could well be returning from a max weight take-off in hot /high / humid conditions on one engine with significant terrain considerations. In that case you would want all the performance you can get!

Below MLW, flying around low flat terrain you may consider the exercise too time consuming or distracting for you to bother with at the time. That's your call on the day.

I just checked the Landing Climb performance figures (Gear Up, One Engine Inoperative, Go-Around Thrust, bleeds On) in the performance manual.

The B738 manual with Engine Bleeds Off allows you to increase the gross climb gradiant 0.2% (i.e. from say 3.0% gradient to 3.2% gradient).

The B734 makes no mention of a Bleeds Off climb gradient credit. Obviously it would be in the same order as the B738 (wouldn't it??).

I suppose it would be good to sit down one day and become familiar with some of the relevent numbers in the book with regards to gross weight vs climb gradient. Then you'll have a better idea whether or not having bleeds on/off will make or break your day (if you should ever be so unlucky).

cheers.

[Seat1APlease]

In addition to the above:-

Is the APU serviceable?

Do you have time to start it to provide the air for the Pax, are you full, or could they manage a few minutes without airflow?

Do you have time to start it and reconfigure or are you on fire?

All sorts of questions!

[Blacksheep]

You can never have too much thrust available.

Let the APU look after the bleed air and keep plenty of thrust in hand.

[LEM]

I'm with Blacksheep, of course.

But Hudson was asking a good question: How can we "scientifically" decide?

Is anybody provided with such information at his company?

I don't think so, and yes, it's a grey area, as you will have to decide on your gut feeling.

[BLE]

The 737 is very rarely Landing Climb Limited, in 99.9% it is Approach Climb which is the limiting factor for landing.
Most two engine transports are limited in the same way.
Four engine ones are normally limited by Landing Climb.

Blip correctly defines the parameters valid for Approach Climb, but incorrectly calls it Landing Climb.
Landing Climb is with ALL engines running, gear down and landing flaps.

You can "scientifically" decide by using the Performance Dispatch chapter, Volume 1 for the NG versions. Remember to apply restrictions for operations in icing conditions, and you will see the need to configure for bleeds off approach on all but the most powerful versions if you have anything above standard approach climb gradients , or are operating close to MLW.
On WAT charts the same info should be available.

You can use bleeds off approach with or without an operable APU. Minor differences in the procedure, but performance wise the improved climb gradient will be the same.

The classics are even worse off, since most operators do not opt for (read pay) the option of having Performance Dispatch added to Vol. 1.
Then you as pilots are left to dig into the Flight Planning Performance Manual, or even worse, the AFM.
Yeah, and one day pigs will fly..
If you do not have WAT charts, I suspect most of you operating 300 with 20k, 400 with 22k and 500 with 18.5k engines have been way above approach climb limit weights more than once..
Especially if you are CAT II/III operators..

The most accurate, easy, dependable and pilot friendly option is to buy a BLT.

No, not the edible one, but the Boeing Laptop Tool. Or a similar approved product which utilizes AFMDPI data (NG) or AFM perf. charts in a software program which gives you instant numbers, correct for the location and condition, and presented on a laptop.

But they cost money, and that is the primary reason why most companies do prefer to give pilots the mushroom treatment when it comes to performance.
:p