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Aviation History
1966
1966 - 0077.PDF
International, 13 January 1966 51 V, V2 AND ALL THAT Part 17 of C.C.J.'s "V" Classifications THE touchdown speed (Vtd), plus the minimum controlspeed on approach to land (Vmm), which was dealt with inPart 2*, really complete the definitions of the operational landing speeds and the certification speeds to which they are related. However, not all approaches to land are successful and so it is essential to mention the two forms of overshoot speed. With regard to these it is certainly comforting to know that the certificating authorities have taken so much care of the pilot in extremis—and, indeed, are (at least in the U.K.) work- ing away to introduce even more stringent safeguards. Fortunately, as the requirements are all associated with a comparatively lightly loaded aircraft (max. landing weight), there should be little difficulty, from a design point of view, in compliance. Dealing first with the certification aspects of the case, in establishing the discontinued approach speed in terms of the ICAO PAMC.t it is assumed that the aircraft is in "the estab- lished configuration which would be used during approach down to the point where a decision to land would be made when operating in limiting visibility conditions" (this could be full flap or something less than full flap, depending on the air- craft and the operational technique recommended). It is then assumed that, from this position, the descent is checked and 15 seconds elapse during which time the gear is retracted and flaps are reset; after the 15-second point, the aircraft should, at maximum landing weight, have the performance to climb, one- engine-out, at a gradient of 2.4 per cent (fours), 2.3 per cent (threes) and 2.1 per cent (twins). These figures are related to the initial climb-out gradients of the take-off case; they are, how- ever, a little less, the corresponding take-off figures being 3 per cent for fours, 2.7 per cent for threes and 2.4 per cent for twins. BCARs have recently been under revision in connection with the discontinued approach speed and the latest wording shows significant variations from the above ICAO requirement. In particular: (a) The new "contingency power" (i.e., greater than take-off power) can be used to show compliance with the discon- tinued approach climb gradient. (b) Automatic configuration changes of flap and/or spoilers are permitted so long as no "gated" position is passed. (c) To guard against sink, the stalling speed of the new con- figuration (i.e., after flap resetting) must not be greater than 1.1 times the stall in the landing configuration. (d) There must be at least one second between the completion of movement of one auxiliary control and the initiation of movement of the next. (e) The speed must not be less than Vmei plus 5kt As this series of articles was intended to be written round the international (i.e., ICAO PAMC) requirements, and as the whole point of it has been to produce short definitions, I am not including the above in the wording at the end of this section. There is, however, an exception in the case of "Vmri + 5kt" (see Note 1 at the end of the definition) because this has proved a very significant requirement—and will be even more so with the SST. Turning now from the certification aspects to the operational aspects, I believe that the discontinued approach speed is best stated in terms of Vu, or Vtt plus, in exactly the same way as recommended in Part 15 of this series for the approach and landing and in parallel to that recommended in Part 7 for the take-off. The calculation of Vtt (which will normally be at least 1.3 times the stall—hopefully the V.i* stall) will provide a satisfactory speed for the initial configuration, power and angle ot attack; however, an additional margin is usually required to take care of the retraction of flap and change in angle-of-attack: an additional speed increment will therefore be needed for the operational" discontinued approach speed. There appears to be no established mnemonic for the dis- continued approach speed. It would not be difficult to invent one—Vda, Vos, Vma, Vab, or Vga (discontinued approach, over- shoot, missed approach, abort, go-around)—but I think that it is worth preserving a close connection with the take-off climb so that cockpit procedures for flaps, power selections, etc, fall as rapidly as possible into line with the familiar techniques of the take-off. With this in mind, therefore, I am not suggesting any additional V speed for this (or for the landing climb speed which follows) but simply the use of "Vtt plus 10" or whatever the increment should be for the type in question. Definition 22.1 The Discontinued Approach Speed is the speed recom- mended for initial climb-out after a missed approach initiated at the decision height For certification purposes it is so selected that, at maxi- mum landing weight, with the critical engine inoperative, with the remaining engines operating at maximum power, and with the aircraft in the configuration achieved 15sec after reaching the decision height, the minimum gradient of climb is 2.4 per cent (fours), 2.3 per cent (threes) and 2.1 per cent (twins). For operational purposes it is selected at a fixed increment above Vu provided that the gradients achieved are not less than those given above. Note 1: In British Civil Aviation Requirements the dis- continued approach speed must be at least 5kt above Vmoi. Note 2: The decision height in this context is the lowest height at which, during an approach in limiting weather minima, a decision to land would be made. PAMC 7.3.4 ICAO Doc. 8458-AN/881, page 33. Draft BCAR D2-4 Sect 4.5 and App. 1.6 FAR 25.121(d). There is, in both the US and the British regulations, a "landing climb" (US) or a "balked landing" (UK) speed as well as a "discontinued approach speed." The two concepts are closely allied but the landing climb speed is relative to all- engines operating and a minimum gradient of 3.2 per cent (fours, threes and twins) against 2.4 per cent to 2.1 per cent for the (engine-out) discontinued approach speed. Of the two designations referred to above, I prefer the expression "landing climb" to "balked landing" because it is more descriptive in itself and also because the word "balked" is not very well used (or spelt) and could be confusing, especially to the foreigner. The landing climb speed does not appear in the ICAO recommendations, but I should like to think that (at least for the time being) this series covers all the speeds which a pilot may meet in his operations. Until now he has not very often found himself overshooting from runway level but, as we get into the all-weather categories 2 and 3, where landings are attempted in patchy fog, the pilot will want to know just how his aircraft will behave if he has to open up at the last minute—will it sink, yaw off the localiser, or climb happily from just above the stall? Undoubtedly these will take on a new significance and I am therefore including reference to the landing climb even though it again means departing from the •See Flight for January 30. 1964. fDoc. 8458, 7.3.4, page 53. JThis wording obviously invites the use of the expression "decision point." As, however, this might lead to confusion with Vi, the speed associated with the decision point on the take-off, I believe that it is important to refer to it as the decision height; this avoids the confusion and at the same time lines up with the terminology used in the proceedings of the ICAO All Weather Operations Panel.
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