Boeing 737 selection of Landing flap in the normal circuit

[Centaurus]

The Boeing 737-200 FCTM (then called the Pilot Training Manual) December 1982 contained the following advice on flying a normal visual circuit pattern.
Selected text included "Enter downwind with Flap 5 and 170 knots. Maintain a track parallel to the landing runway approximately one and a half mile abeam. Just prior to turning base leg extend the landing gear, position the flaps to 15 and slow to 150 knots. Arm the speed brake, check for the green lights and call for the "landing checklist to the Flaps."

Retrim the stabiliser to maintain zero elevator forces at all times. When turning on base leg, extend the flaps to 25, adjust thrust as required, slow to 140 knots while descending 600-700 FPM on the base leg. Extend the landing flaps turning final, reduce speed to Vref plus the wind corrections and call "Complete the landing checklist."
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The 737-300 FCTM date 1 October 1997 gives this advice for downwind and base leg. "Enter downwind with flaps 5 at flaps 5 maneuvering speed. Maintain a track parallel to the landing runway approximately 1.5 NM abeam.
Prior to turning base, extend the landing gear, select flaps 15 and slow down to flaps 15 maneuvering speed. If the approach pattern must be extended, delay lowering the gear and selecting flap 15 until approaching the normal visul approach profile. Turning on base leg, select flap 25 and adjust thrust as required, to maintain flaps 25 maneuvering speed while descending at 600-700 FPM. Extend landing flaps prior to turning final. Allow the speed to decrease to the proper final approach speed and trim the airplane. Complete the landing checklist.
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The June 2016 737CL FCTM changes the pattern to say:

Typically fly at an altitude of 1,500 feet above the runway elevation and enter
downwind with flaps 5 at flaps 5 maneuver speed. Maintain a track parallel to the landing runway approximately 2 NM abeam. Before starting the turn to base leg, extend the landing gear, select flaps 15, arm the speedbrake, and slow to flaps 15 maneuver speed or approach speed plus wind
additive if landing at flaps 15. If the approach pattern must be extended, delay lowering gear and selecting flaps 15 until approaching the normal visual approach profile. Turning base leg, adjust thrust as required while descending at approximately 600-700 fpm.
Extend landing flaps before turning final. Allow the speed to decrease to the
proper final approach speed and trim the airplane. Do the Landing checklist. When established in the landing configuration, maneuvering to final approach may be accomplished at final approach speed (VREF plus wind additive)
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I understand that for the B737NG equivalent pattern, landing flaps are selected before turning base and then the landing checklist is called.
My question is when and why the original pattern was changed from selection of landing flaps turning final (which seems logical to me) to the current Boeing 737 advice to select landing flaps before turning base?

Also the original Boeing advice to select landing gear down and flap 15 while downwind and then call "Landing checklist to flaps" (again was a logical call IMHO) was later changed to waiting until landing flap selected and then calling for the whole landing checklist. I was advised the advice to select landing flaps downwind was that the landing checklist could be completed rather than the split checklist used when the 737 first came into service.

That being the case surely that means the tail is wagging the dog In other words changing the configuration to suit a checklist. To have landing flap downwind with the commensurate relatively slow airspeed more in line with a Navajo Chieftain, seems a clumsy way of flying a jet transport.

[B2N2]

I think you need to look into requirements for 'stabilized approach' and no further configuration changes below a specified altitude.

[A37575]

Every company has its own criteria for a stable final approach. Are you saying that the original Boeing philosophy circa introduction of the first Boeing 737 in the late Sixties did not address the requirement for a stable approach?
One of the current Boeing requirements states: "An approach that becomes unstabilized below 1,000 feet above airport elevation in IMC or below 500 feet above airport elevation in VMC requires an immediate go-around".

As the discussion is about a visual approach and not an instrument approach, then as per Boeing, the aircraft must be stable by 500 feet. Thus selecting landing flap before turning base on a visual approach as a reason to be stable before being established on final, is not valid. It certainly can cause a problem for following traffic.

[B2N2]

Originally Posted by A37575

Thus selecting landing flap before turning base on a visual approach as a reason to be stable before being established on final, is not valid. It certainly can cause a problem for following traffic.

In the original :

contained the following advice on flying a normal visual circuit pattern

This is why you can learn how to fly from a book but you can't learn how to be a pilot from a book.
Obviously at some point doing some "pilot stuff" is required.....such as adapting to conditions...like other traffic..

[Jwscud]

When I did base training on the NG, landing flap was taken on base or turning final depending on whether you were high or low. The stable approach gate was 500ft in VMC.

[None]

I tend to agree with B2N2 that it may have something to do with stabilized approaches, though I'm not certain.

I have to learn something from all of the flight safety data that says folks are pressing or not meeting the stabilized approach gates. We have a lot more information/data today than we did back in the 60's thanks to a number of initiatives.

I have to remember that these stabilized approach gates are my last chance to meet the requirements. They are not the goal. I'd rather be fully configured with checklists complete prior to 1000 on a visual approach than be hoping I can bleed off the speed enough to meet the 500' gate.

If Boeing is also thinking this way, then they may have decided it is much safer to get everything done early and then be able to fly the jet without the distraction of a checklist.

As A37575 states, "Every company has its own criteria for a stable final approach." My company is seriously considering moving the gates back to a point earlier in the approach...because the flight safety data being received indicates this may be a prudent move. And my leadership is telling us that unstabilized approaches are often a key ingredient for a runway excursion.

[RAT 5]

The June 2016 737CL FCTM changes the pattern to say:

Before starting the turn to base leg, extend the landing gear, select flaps 15,
Turning base leg, adjust thrust as required while descending at approximately 600-700 fpm.
Extend landing flaps before turning final.

I understand that for the B737NG equivalent pattern, landing flaps are selected before turning base and then the landing checklist is called.

I don't understand your question. Your conclusions seem to contradict what you have already posted from FCTM.