Vehicle Crossing Under Low Visibility
You are the tower controller at a single-runway airport, runway 09/27, 2,600 m long. Low visibility procedures are in force, RVR 600 m, and the CAT I minima are 550 m. An arrival, SEJ 205, is on a 3 NM final and cleared to land. A follow-me vehicle, 'Follow 1', is holding at holding point B and requests to cross runway 27 to reach the apron. Earlier you gave 'cross runway 27 at B' to a different vehicle, 'Follow 2', which has now reported clear. The ground controller is on a break and you are working tower and ground positions together. The ATIS is 20 minutes old and still broadcasts visibility 2,000 m. The driver of Follow 1 is newly qualified and is on the frequency for the first time. There is no stop bar at holding point B and no surface movement radar.
1. State your actions in the first 30 seconds, in order of priority.
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The first priority is the aircraft on final, because it is the party that cannot stop quickly. Tell SEJ 205 to go around: 'SEJ 205, go around, fly runway heading, climb 3000 feet.' Do not wait to see whether the vehicle crosses in time. Once the aircraft is committed to the go-around, instruct Follow 1 to hold position: 'Follow 1, hold position, I say again, hold position.' Then ask Follow 1 to confirm its exact position relative to the holding point, because the driver is new and may already be past the marking. Notify approach control that SEJ 205 is going around so the aircraft is sequenced again and other arrivals are protected. Log the time, the instruction and the readback. Only after the aircraft is safely climbing and the vehicle is confirmed stopped do you consider crossing, and then only with explicit two-way contact and a positive position report. The order matters: aircraft first, vehicle second, paperwork third.
2. What do you say to Follow 1, and how do you phrase the crossing clearance to avoid the earlier ambiguity?
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The earlier phrase 'cross runway 27 at B' is ambiguous in this context, because 'at B' can be heard as the location where the instruction applies rather than the point from which the crossing begins. The presence of two follow-me vehicles on the same frequency makes it worse. The safer form is to name the vehicle, state the restriction first, then the clearance, and require a readback: 'Follow 1, hold short of runway 27 at holding point B, call me when holding.' Once ready, 'Follow 1, cleared to cross runway 27 at B, report runway vacated.' After crossing, 'Follow 1, report fully vacated and on the apron.' For Follow 1 specifically, include the runway designator and the words 'cleared to cross' rather than a bare 'cross'. Ask the driver to read back the full clearance, including the runway number, and challenge any readback that omits it. A new driver should be given the clearance in a slow, plain form and the readback checked word for word.
3. Identify the systemic failures and the changes you would recommend.
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Several defences failed at once. Single-controller operation of tower and ground during low visibility removed the cross-check that normally catches a misheard clearance. The absence of a stop bar at B removed the physical barrier that stops a vehicle from entering the runway without a clearance. The ATIS was 20 minutes old and still advertised 2,000 m visibility, so the driver's mental model of the conditions was wrong; the ATIS should be updated whenever RVR changes to a lower band or LVP are activated. Two vehicles with similar callsigns on the same frequency increased the chance of a misidentification. The new driver had no local briefing on LVP procedures. Recommendations: prohibit simultaneous tower and ground responsibility during LVP; install a stop bar or a mandatory stop-and-report procedure at B; require an update to ATIS on entry to LVP; brief follow-me drivers on frequency discipline and readback; and record the event for a local occurrence review.