B737NG- Setting Flaps With Higher Speed
 

Hi Guys,
I read here that Boeing Recomends setting flaps 20 kts less than the speed limitation for the selection. Example 250 Kts limitation, use 230 Kts. Do you know where Can I find this Document? Because the FCTM said that it's not recommended to use flaps as Speedbrake or with higher than maneuvering speeds.

I guess the reason is to have some margin against the flap set limit airspeed, in case of gust. Not sure, does the B737 have a Flap Load Relief system?

- it would help if you could tell us where you found this.

I havn't get them at hand, but I would think its in the bulletins sent by Boeing, there has been an alarming increase in flap carrier and flap track cracks discovered.

Isn't it just saying, for fatigue avoidance purposes: ideally select Flaps out at min maneuver, else at no more than limit -20?

We have a company requirement not to select flap until 10 knots above the manoeuvring speed. I don't know that it's a Boeing recommendation, though.

Mr Boeing warns against using flaps as speedbrakes. Is this not what he means?

Our Company is trying to introduce the habit of setting flaps with maneuver speed to preserve Flaps, But sometimes is impossible because We have some Stars we cannot do with the standard pattern, I remenber I read here the 20 Kts less than the limit as Boeing Recommendation. I'm not able to find this document.

What problems are you having with Stars? I cannot recall any 'advice' other than as above and '10kts above manoeuvre speed' is quite common.

The problem is that sometimes you have to do impossibly steep descents at comparatively low speed (below 250, somewhere above 225 or so), for example at non-radar controlled airports with high minimum crossing altitudes - unless youre visual you will be stuck high up and unable to for example make a straight in ILS (we got a couple of airports like this in our route network unfortunately) - speedbrakes are useless at low speeds, and flaps 5 and 230 knots just work so brilliantly ;)

Then you are doing it incorrectly. Assuming it is angle of descent you wish and not just rate your best angle is achieved by using the maximum available flap at the minimum available groundspeed. Flap 5/230 undoubtably gives you a better rate but not angle. Try it.

We have the same requirement within our company SOPs (737). Actually it's recommended to select flaps at min. manoeuvring speed for that particular flap setting. It is to preserve the flap mechanism. Works quite well and we just learn not to use flap as speedbrake. There are other options to get down, first of all increase airspeed (when altitude/track miles are sufficient), second use speedbrakes (altough they are ineffective at low speeds), third is to configure with flaps (and then we also decelerate to the manoeuvring speed) and the last resort is to fully configure in the landing config.

Most efficient way to descent quickly <10.000ft is to fly 250kts with speedbrakes flight detent and gear down... works very well if you're suddenly cleared for a visual circuit and you just lost 15 track miles or so :)

the last resort is to fully configure in the landing config.

Caveat - not flown the NG, only the Classics. This idea works very well. Often used a high overfly coming into Cairns from Darwin to minimise the discomfort of turbulence. Over the upwind threshold and into the circuit at around 10-11,000 feet, configuring to gear/25. Reasonably tight circuit. Spin up and reconfigure to land going around base ending up in the slot on final. Good, clean fun and worked a treat, saving a fortune on passenger amenity items.

As I recall, a bit better than a mile a thousand.

hmm. I have a vague idea that you can get some sort of variation on the maintenance schedule if you pass on this recommendation as part of your SOPs. I seem to recall some management type mentioning this.

Big caveat; its only a distant memory and I have nothing to back it up.

pb

When it wouldn't save any maintenance costs, I think no airline will enforce this SOP... So I think your statement is quite believeable