B737-300 Non-Normal landing speed query

[Centaurus]

In the B737 FCTM page 6.8 there is reference to bug settings for non-normal landings. It states:
"For non-normal landings, position two white rerefence bugs at VREF and single white reference bugs at the flap 5 maneuvering speed and the flap up maneuvre speed".

So, if for example you are doing an all-flaps up landing what is the reason for setting a reference bug at the flap 5 maneuvre speed?

Also at Non-Normal page 6.9, referring to all flaps up landing final approach, Boeing state "Engines will be at low idle speed due no flap extension...when engines are near idle rpm, time required for engines to accelerate is longer than normal".

However, when reading Boeing Volume 1 (Engines, APU, Engine System Description), under sub-heading Idle RPM, it states that the minimum engine speed for all flight phases is high idle. There is nothing about the idle RPM being affected by flap non-use.

Seems contradictory to me. Any answers, please?

[LEM]

High idle is not affected by flaps position. What they mean is that for a flapless landing you won't really have low idle (which you get 4 seconds after touchdown), but a low power setting on the approach, because of the clean wing low drag.

[HotDog]

Centaurus, I am not familiar with the 737, however on the 747 the FCU condition motor will run automatically to the flight idle position when the aircraft is in the landing configuration (flaps extended to 25deg. or more). The extra fuel supplied in this position will ensure that RPM will not fall below that required to assure proper engine acceleration capability. After touchdown the ground safety relay will signal the motor to run to ground idle with a six second delay. On a flapless landing approach, the throttles should not be retarded below 55% N1 until touchdown. For interests sake, Vref30+40 has to be bugged up and the landing run required at max ldg. wt. for the 747-200 is 10,000ft.

[LEM]

And, for interest sake, Freud has described very well the need to compensate for the lack of size of one's attributes with the size of an artificial substitute.

:p :D :p

[HotDog]

LEM for an alleged airline captain, you ask some real dumbass questions about aviation and your answers are not any better either.

Personally, I'm considered a bit rude because I intervene (not by declaring "I have control", but by "helping" on the yoke) almost always as soon as I have the feeling that the FO is going to make a bad landing.

I think we have another Walter Mitty in our midst!

:yuk: :rolleyes:

[LEM]

I just checked your profile, HD, and I'd like to say ... sorry, even if you started this little game by asking me if I fly airplanes/heavy jets, remember?

My father too retired a few years ago, and I know what it is to loose the big toy forever...

OK, still friends?

:ok: LEM

[HotDog]

OK LEM, I have no desire to engage in verbal battles on personalities. In a career as a professional flight engineer, 33 years and 20,000 hours + on various jet aircraft (CV880, B707, L1011, B747-100,200 & 300 pax and freight) I do think I have a little knowledge in the aviation field and I hate bullsh!t. Yes, I do miss my big toy, I miss having my hair cut in Dubai, I miss the mussels and beer in Brussels and the pig's knuckles in Mainz. However, most of all, I miss flying with my professional colleagues. Pprune keeps me in the loop and I avoid posting facts that I am not sure about. Cheers, HD.

[QAVION]

"Seems contradictory to me."

To say the least!

Are both volumes provided by your company (for use on the flight deck)?

What sort of engines are fitted to your aircraft?

I'm not familiar with the 737-300, but the text for one of the larger Boeing technical manual reads:

"Ground Idle/Flight Idle Select Solenoid

If energised, the engine idle is low (ground idle). If de-energised, engine idle is high (flight idle). The solenoid is always energised (ground idle) in the air or ground mode, except during landing approach..."

Assuming Boeings are pretty much standard, perhaps your second manual has omitted the "except" part?

I wish Boeing would simply stick to two terms. High Idle and Low Idle... and not mention Flight Idle, Approach Idle, Ground Idle, etc.

Regards.
Q.

[HotDog]

If energised, the engine idle is low (ground idle). If de-energised, engine idle is high (flight idle). The solenoid is always energised (ground idle) in the air or ground mode, except during landing approach..."

That is correct and exactly what I said in my post above. I also believe the 737 to be not much different. Selecting landing flap, will cause the FCU to schedule flight idle until touchdown with a 6sec delay before establishing ground idle RPM.

The following from my GE CF6-50 notes on the subject:

Engine control is provided by the MEC main engine control and incorporates a flight/ground solenoid which selects a higher flight idle(+14%) when airborne and flap is set at 25 degrees or more. Engines remain in flight idle for 5 secs. after touchdown, after which the solenoid in the MEC is energized and GND idle is selected.

[Ugly Jet Captain]

Wow....I have over 10,000 hours in 737's and I thought they just meant when you have no flaps out the power required to maintain V ref is very low so use caution.

Don't over think it. It ain't that hard.

The ref speeds you are bugging for should be for the flap setting you are using to land. I see no need to bug for any other flap settings. Use 210 to manuever unless your over 117 K and then use the 220 number. It has proper buffet margins in both cases.

Simple enough?

[HotDog]

The caution is to be aware of the spool up time required in case of a go-around. Obviously differs with engine type. What Vref do you bug up in a 737 for a flapless landing? As it's not supposed to happen, Boeing did not have flapless landing drill in the QRH for the Classic 747 but we did practice one in the sim during our conversion course in Seattle and the bug setting was Vref, flap30+40kts.

[LEM]

In a 733, for an ALL FLAPS UP LANDING, set Vref 40+55, which gives roughly 185kts.

Regarding the approach technique, of course on a twin you can't play with the engines, but on 3-4 engines you can idle the center-outers, and it will be easier to maintain your speed and to get goaround power faster.
HD please confirm the above (which personally I've never done!).

[HotDog]

No, the stipulation is; maintain 55% N1 till touchdown to give you safe missed approach capability. No problem with speed control, you can always use spoilers anyhow. We never had to do one in my 33 years of flying and it wasn't a CAD requirement to practice it in the simulator either.

[LEM]

I found that information in "Handling the big jets" by D.Davies (1971), a classic on this subject - sometimes obsolete, after more than 30 years...

High lift devices-> Complete failure case-> page 96:

Fly a low, flat final approach. On four-engined types speed control is improved by idling the outers and flying the approach on the inners only (on a three-engined type idle the centre engine). As the drag is so low there will be plenty of thrust available and larger thrust lever movements are possible without upsetting the speed.

Has anybody used this technique in the past?

[HotDog]

Oh yes D.P.Davies, first published 1967 and as you so rightly point out, somewhat obsolete. The 55% min. N1 on the JT9 equipped 747 Classics was a Boeing recommendation. Sure you could play with the thrust levers for speed control but idling the outers would most probably run the inners at more than 55% N1 so why not follow Boeing's advice. As I said, we only did flapless approach practice in the Boeing simulator during initial conversion in 1979 and that's the way we were taught to carry it out. Also modern engines have a faster spool up time these days so maybe Boeing philosophy has also changed?

[QAVION]

Centaurus....

I checked the wiring schematics for one airline's 737-300's (P&W-engined) today and there was no input from the flaps to the Fuel Control Unit solenoid.

I don't think my findings prove conclusively that your -300 aircraft are the same. I think you need to contact your engineering department to find out the specific details of your own aircraft. There may be variations between airlines and between aircraft. On another airline's 747-800, I saw that there was a flap input (at least to the EEC... what the EEC did with it, I couldn't tell by looking at the diagram).

Regards.
Q.

[LEM]

In his statement Davies did not refer to the 747 classic in particular, but probably to the 707, 727, Trident and others...
He says the 720B was so powerful!... maybe on that type that trick helped...

[Centaurus]

Qavion. Thanks for going to all that trouble. Having looked closely at the Non-Normal QRH on flaps up landings, I am beginning to think that LEM is right and that where the word low idle is used (in associated paragraphs on flapless landings), it probably means that lower than usual approach power is needed to lack of drag. Not to be confused (well, I certainly was) with an engine condition known as high idle and low idle.

I still don't know why in a flapless that the Flap 5 maneouvering speed is set on a bug.