Descent Planning into a Shared Runway with a Tailwind
You are the pilot flying a twin turboprop at FL240, 96 NM from the destination VOR, cleared to descend at pilot's discretion for an ILS approach to runway 27. The ATIS reports surface wind 240/18 gusting 28, runway 27 (3000 m, dry, slope 0.5% uphill in the landing direction), and the ILS glideslope is 3.0°. Your aircraft's landing performance chart shows a landing distance required of 1180 m in still air at the expected landing mass, with a 10% additive for a wet runway (not applicable today). The operator's policy requires a 15% margin over the landing distance available. Your current TAS is 250 kt, and you plan to cross the threshold at 120 kt. Traffic ahead is a heavy jet whose wake turbulence the tower warns about. Fuel is not a constraint.
1. Using the reported wind, estimate your groundspeed on final approach and the resulting headwind/tailwind component on runway 27. Is there any performance concern for the landing roll, and how does the 15% policy margin interact with the gust factor?
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Runway 27 bears 270° magnetic; the surface wind is 240°, so the wind is 30° off the runway centreline from the left. The headwind component is 18 × cos 30° ≈ 15.6 kt, and the gust component is 28 × cos 30° ≈ 24.2 kt. So you have a headwind, not a tailwind, on the landing direction - the apparent tailwind concern is unfounded. Groundspeed at 120 kt IAS on final is roughly 120 − 16 ≈ 104 kt in the steady wind, gusting to about 96 kt.
Landing distance: the chart figure of 1180 m assumes still air. A headwind reduces ground roll, but do not credit it in the certified calculation unless the chart explicitly provides a headwind correction. The 15% policy margin gives a required 1180 × 1.15 = 1357 m against 3000 m available - comfortably inside limits.
The real judgement issue is the gust spread of 10 kt: approach speed should be increased by half the gust factor (about 5 kt) to 125 kt, and this raises the landing distance slightly. Even adding a conservative 10% for the higher approach speed, 1180 × 1.1 × 1.15 ≈ 1493 m, still well within 3000 m. The uphill slope of 0.5% increases landing distance marginally; check the chart's slope correction, but it does not change the conclusion.
2. You are 96 NM out at FL240 and need to lose height for the approach. With a 3° glideslope and a planned 3 NM final, compute the approximate descent profile and state whether an idle descent from FL240 will meet the profile without speedbrake. What would you do if ATC keeps you high?
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A 3° glideslope corresponds to about 318 ft/NM. From 3 NM final at roughly 950 ft above the threshold, you need to be at approximately 24000 ft at 24000/318 ≈ 75 NM from touchdown, i.e. about 78 NM from the threshold including the 3 NM final. You are 96 NM from the VOR, so an immediate idle descent is required - you have effectively no slack. At 250 kt TAS and a 3° path, required rate of descent is groundspeed × 5 ≈ 1250 ft/min (using the 5 × groundspeed rule for a 3° path).
An idle descent in a twin turboprop typically achieves 1500–2000 ft/min at high speed, so the profile is achievable but tight; any level segment or ATC restriction will put you high. If ATC keeps you high, options in order of preference: request a lower level immediately and advise "unable profile"; ask for a longer final or a vector to lose height; use speedbrake if fitted and within limitations; and as a last resort, plan a go-around rather than forcing an unstabilised approach. Do not accept a late clearance that requires exceeding 1000 ft/min below 1000 ft AGL or an unstabilised approach at 500 ft.
3. Tower warns of wake turbulence from a heavy jet landing ahead. Where should you aim to touch down relative to its flight path, and how does the gusting crosswind affect your handling plan?
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Wake vortices sink and drift with the wind. With a 30° left crosswind component of about 9 kt (18 × sin 30°), the heavy jet's vortices will drift to the right of its flight path and sink below it. Plan to touch down beyond the heavy jet's touchdown point and stay upwind (left) of its centreline where possible, aiming to land at least 2–3 NM behind it or after a suitable time interval. If the tower offers a go-around or a hold, accept rather than accept a tight spacing.
Handling: the gust spread of 10 kt means approach speed +5 kt, and the crosswind of 9 kt gusting to 14 kt is well within the aircraft's demonstrated crosswind, but the gustiness demands active into-wind aileron and rudder. Fly a stabilised approach to 500 ft; if the gust causes more than a 10 kt deviation or the sink rate exceeds 1000 ft/min below 500 ft, go around. The wake encounter risk is highest at low level on a parallel or following path, so keep the touchdown zone aiming point and do not float.