Displaced Threshold, Twelve Knots of Tailwind, and a Late Go-Around
You are flying a 2,550-lb single-engine airplane into a 3,200-ft by 60-ft paved runway with a threshold displaced 400 ft. The AFM shows landing ground roll of 1,000 ft and a 50-ft obstacle distance of 1,525 ft at maximum weight, sea level, ISA, no wind. Field elevation is 500 ft, OAT 25 degrees C, surface dry. Reported wind is 090 at 12 kt; you are landing on runway 27. Approach speed is 65 KIAS. On short final at about 300 ft AGL you are 20 kt fast, high, and the tower reports a 15-kt gain on the anemometer.
1. Compute the landing distance available and the estimated distance over a 50-ft obstacle, then state whether the approach should be flown.
Read the worked answer
LDA = 3,200 - 400 = 2,800 ft.
Tailwind: a 12-kt tailwind on a 65-kt approach raises ground speed to 77 kt. Energy and therefore distance scale with the square of ground speed: (77/65)^2 = 1.40.
- Ground roll: 1,000 x 1.40 = 1,400 ft
- Over 50 ft: 1,525 x 1.40 = 2,140 ft
That is 2,140 / 2,800 = 76 percent of the available runway before any correction for temperature, gradient, or float.
Judgment: the book numbers are demonstrated maximum-performance values flown by a test pilot on a dry runway, with no float and prompt braking. A line pilot flying a real approach will not reproduce them, and a tailwind makes the airplane float, so the touchdown point drifts down the runway. A 660-ft cushion is not a margin - it is the difference between a good landing and an excursion. Either land on the opposite runway (a 400-ft displaced threshold on one end usually means the reciprocal has usable pavement), or expect to go around and divert. Fly the approach only if you are committed to touching down in the first few hundred feet past the threshold and are willing to abandon it.
2. What does the 400-ft displaced threshold change about your flight path, and what mistake does it commonly induce?
Read the worked answer
The displaced threshold does not move the pavement - it moves the legal touchdown zone. The full 3,200 ft of asphalt is still there for rollout and for taxi, but you must cross the displaced threshold at or above roughly 50 ft and touch down beyond it.
The common error is treating the visible pavement before the threshold as usable landing distance and aiming at the numbers - which puts you on the runway early, with the wheels down in the overrun area and a shorter rollout available. On a 3,200-ft runway with a 12-kt tailwind, that error is compounded: you need every foot of the 2,800 ft of LDA and none of the 400 ft of displaced pavement.
Fly a stabilized approach to a aim point several hundred feet past the displaced threshold, and add the displaced distance to your mental picture of where you must touch down. If the aim point is not being made by roughly 200 ft AGL, the answer is a go-around, not more back pressure.
3. At 300 ft AGL, fast and high, with a shear report and traffic still on the runway, describe the go-around and the specific risks the tailwind creates during it.
Read the worked answer
Go-around: power to full, carburetor heat cold, simultaneously reduce pitch to arrest the descent and hold the airspeed at the target climb speed - you do not want to trim into a climb until you have positive rate. Establish a positive rate, then retract flaps one increment at a time (going from full flaps to zero in one movement causes a sink that at 300 ft is unacceptable), retract the gear if it is down, and fly the published or assigned climb path. Advise the tower.
Tailwind-specific risks:
- Ground speed is 12 kt higher than indicated, so the airplane covers more ground during the several seconds it takes to arrest the sink and reconfigure. The 300 ft of altitude converts to fewer feet of horizontal clearance than it looks like.
- The same wind gradient that produced the 15-kt gain can reverse on climb-out; expect airspeed to drop and be ready with pitch, not with flap.
- With traffic still on the runway, do not assume the go-around will be flown straight ahead - request a turn or a side-step before the maneuver becomes urgent.
The judgment point: there is no version of this approach worth salvaging. Excess speed plus a tailwind plus a shear report plus a 76 percent runway requirement is a compounding set of problems, and the go-around is the cheapest outcome available.