The Approach That Was Never Stable
Night ILS to runway 09, 7,200 ft, dry except standing water in the touchdown zone; latest braking action is medium. Reported surface wind 090/12 gust 20, but the PM notes a PIREP of a 20-kt tailwind at 1,000 ft and groundspeed is 165 kt. At 1,400 ft AGL you are 1.2 dots right of localizer, 900 fpm down, thrust at idle, with LOC and GS captured. AFM unfactored dry landing distance at the expected landing weight is 4,200 ft. Your operator applies a 1.67 factor and adds 15% for a contaminated runway. Fuel is 2,100 lb, 700 lb above reserve; the alternate 60 nm away is 200 overcast, 5 sm, dry, 8,000 ft.
1. Apply stabilized approach criteria to this situation at 1,000 ft. Is this approach stable, and what is the correct call?
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No. At the 1,000-ft gate the airplane is off the localizer, descending at 900 fpm, at idle thrust, and carrying a tailwind that is increasing groundspeed. A stable approach requires the airplane to be on the correct flight path and track, on speed, with thrust not at idle and no excessive sink, by the operator's gate. This one is outside several of those criteria at once, and the trend is worsening, not correcting.
The correct call is a go-around now, at 1,400 ft, not at the gate. Waiting until 1,000 ft to see whether it settles means the crew will be evaluating a deteriorating approach while close to the ground at night over water-contaminated pavement. The go-around also buys time to answer the more important question: can this runway be used at all tonight?
2. Compute the required landing distance and decide whether the runway is usable.
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Contaminated unfactored distance: 4,200 x 1.15 = 4,830 ft. Factored: 4,830 x 1.67 = 8,066 ft required against 7,200 ft available.
The runway is not usable for planning purposes; the requirement exceeds the available length by about 866 ft. Note how thin the dry case is: 4,200 x 1.67 = 7,014 ft, only 186 ft of margin, and that margin assumes no tailwind, no standing water, and good braking. Medium braking action means the actual stopping performance is worse than the dry AFM data, and a 20-kt tailwind raises touchdown speed and distance further.
The decision follows directly: go around, do not attempt the landing, and divert to the alternate, which is dry with 8,000 ft and better weather.
3. What should you tell ATC, and what fuel considerations apply?
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Tell ATC you are going around and request diversion to the alternate, stating the reason briefly so the controller can prioritize you. Ask for the current alternate weather and any known braking action or wind shear reports enroute; do not accept a hold 'to see if it improves' unless you have recomputed fuel against the alternate plus reserves.
Fuel: 2,100 lb with 700 lb above reserve leaves 1,400 lb of usable margin. A 60-nm diversion should fit comfortably, but the margin is not large enough to absorb a second approach, a lengthy vector, or a hold. The disciplined sequence is: go around, turn toward the alternate, then compute. If the fuel picture becomes tight, declare minimum fuel early rather than after the reserve is compromised. The tailwind that made the approach unstable is also a headwind on the diversion, which is the direction you want.