Fog Landings for Airliners

By OLIVER STEWART

ON one of the days of fog and snow at London Airport, when near-zero visibility had stopped airline operations, a Varsity aircraft penetrated the peasouper and made an automatic landing. It was a reminder of how far experi- ment is ahead of normal practice and of how technical talk runs in front of operational action.

Although there has been talk of all-weather flying and all-weather aircraft and all-Weather air forces and airlines for forty-five years, and although there is going to be more talk on the subject next month at the International Air Transport Association's fifteenth Technical Con- ference at Lucerne, precious little has been done for the ordinary aircraft user. Fog has retained its power of veto on normal operations.

Hundreds of thousands of experimental fog landings have been made without, so far as I know, a single serious accident; but airline operators recoil from making the final decision to stop messing about with their beloved weather `Minima' and to introduce apparatus to make all-weather operation standard practice.

Perhaps because it happened at London Air- port without special ground equipment and not at some experimental station, the Varsity land- ing may help to give them the courage to take this step and to take it soon.

Their nervousness is understandable. Charging into swirling green fog at 250 kilometres an hour is always terrifying. Experience does little to make it less so. It is doing an injury to instinct to hurtle into the crowding darkness and never to reduce speed as the stuff seems to close in and solidify. Ships, trains and cars can slow or stop, matching speed to visual range. But the fixed-wing aeroplane must career on and its un- fortunate pilot must put his trust in providence and air traffic control and never let the speed drop below a certain figure dependent upon the type of machine. Worst of all, he must eventually go down through it and land.

Because this asks too much of the human ner- vous system, fog flying must in the end turn to black boxes and we shall all—pilots and passen- gers—feel happier when it does. Here auto- maticity is not a slavish obeisance to fancy modernity, but a genuine need. The brain is not made to cope with fog flying. But the black box has been an inordinately long time getting ready to take over.

As long ago as 1918, when I was chief test pilot at a goVernment research station, we were charged with developing a system of all-weather bomber operation. Turn and hank indicators and much other apparatus for flying accurately through cloud and fog came under test and we prepared plans for all-weather landings.

My recollection is that it was at Felixstowe that automatic landings with flying-boats were done, using a hanging stick below the aircraft to measure height and trigger an elevator control mechanism. Certainly it was at Farnborough in the 1920s, at about the time Doolittle was demon- strating blind take-offs and landings in the US, that the famous Lynx Avro work started.

In those early blind landing trials, long before Eurocontrol of the upper air space had been thought of, the positioning of the aircraft above the fog, at 500 or 600 metres, for its final approach, posed difficulties which modern navi- gational and radar equipment have removed. Ingenious methods were tried. A balloon was moored above the fog on which bearings could be taken or smoke shells were fired at predeter- mined intervals of time for showing position and wind strength and direction. All these efforts encouraged F. W. Meredith, in a paper read before the Royal Aeronautical Society in Octo- ber, 1930, to say: 'Air transport in fog is im- mediately practicable: but it involves an element of risk.'

My impression is that, with radio beams and automatic pilots which can be locked on to them, that element of risk has been so attenuated that airline operators should steel themselves to faCe what remains of it. New British aircraft—civil machines like the VC10 and the Trident and military transports like the Belfast—have auto- matic landing equipment and the need is to hasten its application for normal service.

The very proper anxiety of operators that it shall be trustworthy has been respected by its designers. By triplicating the system, for instance (there are other means), and having a comparator which takes note of the majority vote, a defect in, any one channel may be detected and that channel cut out. Because a duplicated system fails to provide this majority choice, it gives no second chance against failure.

My own fairly recent experiences of blind landings in a Canberra using the Blind Landing Experimental Unit (BLEU) system of the Royal Aircraft Establishment were convincing. The final flare-out, which seems simple to human visual judgment and human dexterity when in the clear, is the test. To achieve a perfect tangential touch- down a complex of measurements has to be made continuously as the last fifteen metres of height are lost and the aircraft attitude has to be con- tinuously adjusted by the use of all flying con- trols and engine throttles.

Early systems used sensitive barometric alti- meters for measuring height, but these could never attain sufficient accuracy for this critical manoeuvre. BLEU uses a radio altimeter. When it was demonstrated to me it also used the mag- netic field from leader cables let into the ground for keeping the aircraft along the centre line of the runway; but I am told that forms of localiscr and glide path transmitters are all that are now required.

With BLEU the flare-out is beautifully smooth and accurate. The 'judgment' of the touchdown point is exact and the last moment kicking-off of drift is positively magical. I believe that the the basic technical work is complete and that the moment for the critical change in ordinary operations is at hand.

In low visibility faith in the airliner captain is the ordinary passenger's tranquilliser. He will have less need of that tranquilliser when the black boxes arc also up there in the cockpit.