How does a pilot cope when ground visibility gets really bad?
With the onset of autumn, nights become cooler and moisture condenses: fog, smog, mist, haar, haze! But with the modern equipment now available perhaps only stardust would prove to be impenetrable.
Even nowadays, however, many aircraft types and airlines require visual contact with the runway, making landing in the thickest fog impossible. The newspaper headline “Air traffic disrupted by fog” is not unusual. Landing in the thickest fog is indeed possible, however. This is facilitated by airport procedures and the aircraft’s automatic flight control system – namely the autopilot.
Automation releases pilot capacity for decision making for safe landing from actual aircraft handling. It has been possible to land by autopilot since the 1960s. Finnair has used autolands since April 1965 – among the first airlines in the world to do so. Nevertheless, it has only in recent decades been considered safe to land without visual contact with the runway. Finnair’s Airbus fleet, for example, is officially certified for such landings. Faster air data computers in aircraft and improved accuracy of navigation instruments have made this possible.
Landing without visual contact demands much of the airport, the aircraft and the crew.
Pilots are trained in low visibility procedures on a totally separate training course, which covers the workings of the Instrument Landing System (ILS), runway markings, lights and signs, meteorology, aircraft systems and possible malfunctions, obstacle clearances, standard operating procedures, and operating procedures in the case of malfunctions (in ground facilities and/or in the aircraft).
Simulators provide an extremely realistic environment for practising normal operating procedures as well as malfunctions. Before pilots advance to performing these landings in practice, they must have solid experience of their type of aircraft. Furthermore, an official regulation decrees that low visibility procedures are practised and reviewed at least once a year in an inspection flight using a simulator.
When all of the above-mentioned requirements are fulfilled and the authorities have approved the procedure, the pilot can make a CAT III B no DH approach and landing (Category III B, no decision height). Then the cloud base is not significant, but a runway visual range of 75 metres is required. This visibility requirement ensures that the pilot will find the taxiway and clear the runway after landing.
If each condition is not fulfilled in its entirety, a higher cloud base and visibility (CAT I-III A) are required.
Negotiating a landing in fog has therefore nothing to do with a pilot’s courage. Rather it requires certain equipment on the ground and on the aircraft, and also for the pilot to have the required experience and expertise.
Jussi Ekman
Filed under: Safety, Uncategorized | Tagged: autopilot, fog, landing
