The big difference between flap manoeuvring spd in B737-600(PMDG) and in B737-300?

[Guest adampihavek]

Hi all,I have one question concerning flaps speeds.I compared flap manoeuvring speeds in B737-300(PIC) and in B737-600(PMDG) with the SAME LDG WT(53.4 tons)And it seems to be rather different.I compared FMC computed speeds with tables from AOM for 737-300 and 737-600.In 300, fl. UP manoeuvring spd on EADI was 210kts , 1 was 190 kts , 5 was 180 kts...and this walues are nearly the same like in table in AOM.But pmdg 737-600 (in AOM,there is only written to extend flaps when speed is passing appropriate F symbol,so I could

[dave_paige 11]

First off, you should be comparing the 737-300 to the 737-700 as they are similarly sized aircraft. The 737-600 is much closer in size and weight to the 737-200 or 737-500.

[mburkhard 23]

Adam,the thing is, the B737NG got a new wing over the older B737-300, and that explains why you can't compare their manoeuvring speeds with the same weight. The wings are just not the same... New in this case means more efficient, which means something like more lift and less drag.Regards,Markus

[Guest adampihavek]

Thank you very much for your answer!Ok,but one pilot(B737-300) wrote me once,that common is "decelerated ILS approach" when before turning to the localizer,I should have flaps 5 and spd 180kts(or +10kts -over 53 tons),then when we are one dot below GS,extend flaps 10 and decelerate to 170/180kts and so on to have Vref at 1000ft AAL.But how is it made on B737-600,700?When I would use manoeuvring spds from my first contribution,if I selected flap 5,I would have spd 155 kts and it is quite different from 180 kts above and I

[Guest adampihavek]

Could anyone reply me to my last message? I

[Guest ColdBear]

Adam,As the other members has pointed out there is a big difference in the wing design between the Classic and NG.Also the speeds you are refering to in the -300 seems to be the "Max flap extension speed - VFE".On the NG the speeds on the speed tape is from the FMC and calculated useing the entered ZFW weight and sensed fuel. Regards,Martin

[Guest FreSte]

Hi Adam, I thought to the same question many times and, being not a real pilot (so consider what I'm writing only just a supposition), I've tried to find an answer by myself from what I read and learned about the variuos speeds of each plane.The flap speeds you are referring to, that are the bug speeds shown on the PFD, are the manoeuvring speed for each flap setting. They depend to the aircraft gross weight and they are normally used as reference for scheduling the changes of flap settings due to the several benefits that they allow to get during the flight. In fact, consider that: > For each flap configuration, the relevant manoeuvring speeds are close to minimum drag > In climb the speeds are close to maximum climb gradient > In level flight it provides relatively constant pitch attitudes > The thrust changes are small as flap settings are alteredEach flap setting is associated to another speed figure based on structural considerations. That is the so called Flap Limiting Speeds. These figures are costant (not weight dependant)and are extabilished during the design of the wing so that the manoeuvring speed of each flap setting at the MTOW (max t/o weight) never exceed the relevant flap limiting speed.During the landing, the gross weight of the plane must never exceed the MLW (max landing weight) that is enough lower than the MTOW (at least on the heavy and medium aircraft). It means that, a part the advantages of executing the changes of the flap settings referring to the relevant manoeuvring speed, you could change the flap setting at higher speeds taking care of not exceeding the Flap Limiting Speeds.The considerations above to say: during the final approach, where it should be preferred to complete the final landing configuration of the plane at something like you said an height of 1000 AGL, it should be better to plan properly in time the various configuration changes during the approach. It means that, as you said, you shuold set flap 5 before final turn to intercept localizer, even if you are requested to mantain a speed greater than the flap 1 manouvring speed. Then when you apparoach the OM, you lower the gear and start to configure the plan for the final approach speed (Vref+5...) lowering the flaps step-by-step (5 -> 20 -> 25 -> 30/40) during the deceleration according to the relevant manoeuvring speed.Confirmation or denail of what I wrote from real pilot are welcome.Bye, Stefano.P.S.: Sorry for my not good english.