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.