VC10 and B707 approach speeds' definition
Hello moggiee,
One of the few and minor compensations of having to move from the Rolls-Royce VC10 to the Massey-Ferguson B707-320 was the well-organised Flight Patterns booklet, my copy of which has finally come to hand. It shows that the intervening 36 years and four types had indeed, as you indicated, muddied my memory somewhat.
Quote from me:
"Yes, I'd almost forgotten that [on the VC10] the VAT is config-specific. On Boeings and MD, IIRC, the equivalent to VAT is VREF, but the latter only has one value: that for full flap with full L/E devices. Every combination of L/E devices and flaps has its own increment above VREF. VREF is always bugged on your ASI. You then add any config-required increment for the landing, and bug that as well. During the intermediate approach, as you you extend whatever devices are available, you fly the appropriate increments above VREF - like you do on a normal approach."
Well, in the absence of any manufacturers' documentation for Boeing or MD types other than the old 707, my above generalisation looks fragile, particularly in the light of your response:
"Not so - the performance manual for (for example) a B737-400 will give you a VREF for each configuration - so you would have speeds such as VREF30 and VREF40 where the number in the title indicates the flap setting . Then, using the BA SOP as an example, there will then be (typically) an increment added to that for wind and gust factor - usually something like "half headwind plus all the gust factor up to a maximum of VREF+15". Therefore with a steady 14kt headwind the approach speed would be VREF30+7kt."
However, your source for the B737-400 appears to be the British Airways in-house Performance Manual for the type, which would not necessarily reflect entirely the Boeing equivalent. Although my 1973 edition of the B707-320 Flight Patterns booklet has British Caledonian Airways printed on its cover, the inside pages are simply Boeing, and my simulator and base training were with AA at DFW.
One thing I got right for the B707, as recommended by Boeing, is that there was only one VREF: the one for the standard landing config of Flaps 50 with L/E Flaps. (What was easy to remember was that VREF + 10 = V2 for the only T/O flap setting - Flaps 14. So the initial climb speed on a 1-engine-out G/A was VREF + 10.)
On the intermediate approach, and on finals, all speeds flown with less than Flaps 50 were according to increments added to VREF, which was bugged. So with Flaps 14 you flew Bug+30, Flaps 25 at Bug+20, and Flaps 40 at Bug+10. However, the bit I got wrong was that, for abnormal landing configs, once you'd calculated and bugged the result, all the intermediate flap setings were flown at different increments above the new Bug speed.
I seem to remember that, on the VC10, we stabilised in the landing config using a wind increment of 1/3 wind-speed ** above VAT, provided the increment didn't exceed 15? As you say, the B707 used a wind increment of 1/2 mean wind + gust, but again not more than 15 (and reducing to the gust alone at the threshold).
The B707 speed at the threshold seemed to offer a lot less "fat" than its equivalent on the VC10. No question of closing the throttles at 50 ft on the Boeing...
** Was the wind-speed used for the VC10 calculation the average of the mean and the max?