FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1986
1986 - 3429.PDF
AIR TRANSPORT London ATC handles major failure LONDON A sequence of faults in the London Air Traffic Control Centre's electrical supply sys tem left controllers without radar for 20min or main com puter for nearly two hours on November 15 at the time of day when the "rush hour" was beginning at Britain's major airports. LATCC controls the airspace over England, Wales, and large areas of the English Channel, Irish Sea, and North Sea. The electrical supply is sup posed to be fail-safe, with radar displays, air traffic com puter, and radio/telephony (R/T) supplied separately from a bank of the Centre's own generators. In addition, the equipment switches auto matically on to a battery sup ply if the generator supplying it fails. This is arranged by having the generators' AC supply fed through rectifiers to convert it to DC; at that point the batteries can switch in if required; then the supply is fed through inverters to re convert it to AC for running the equipment itself. That is not all. In case the rectifiers or inverters fail, the generators can supply the equipment direct via a bypass circuit which can be manually switched in. The fault confounded the system. Between the final inverter in the system and the equipment itself is a capacitor which takes out peaks in a current which is normally steady. The capacitor in the radar line failed, and since it is downstream of the batteries there was no automatic alter native power source to supply the radar. The reason for the capaci tor fault may never be known, because it shorted to earth and completely burned out. The surprise is that capaci tors, if they fail, usually fail "open circuit", that is the cur rent still flows and the only impairment is that the device does not perform its normal function, which is not a crit ical one. The capacitor failure took place at about 0630, and the radar went out but the R/T remained serviceable and so did the main 9020 computer. However, the computer- controlled printers which pro duce the flight progress strips from aircraft flight plans also stopped working. Producing these strips is the computer's most vital front-line function; they are presented to the con trollers at the sector radar screens to warn them what is coming into their area so they can plan aircraft movements. The printer failure was not immediately a problem because the progress slips are produced 40min ahead of requirement. LATCC staff set about switching the radars on to the alternative circuit. Some of the radar displays had been successfully restored to oper ation when the alternative direct circuit supply also tripped out, and so did the generator supply to the com puter; but the computer auto matically switched, as it should have done, on to its battery supply. The battery supply is designed only to last 30min, normally more than enough time to restore an interrupted power source. But at this early hour there were not enough authorised technicians avail able to deal simultaneously with the several problems, and it was more than 30min before supplies to the com puter could be restored, so it shut down. Despite all that was going on, radar screens were func tioning once again within 20min of going blank. How ever, once the computer has shut down it can take more than an hour to restore it to full operational capability when power is once again available. So there was an extended period during which computer-produced flight progress strips were not avail able to the controllers. During this period the ATC assistants had to revert to receiving written flight plans and producing flight progress strips manually. This, like the loss of radar, means that the air traffic flow had to be slowed down as much as pos sible. That entailed calling airports all over the country to tell them to stop aircraft taking off; delaying the clear ance of flight plans from air craft filing to come to England; telling adjacent regional control centres to hold aircraft which were about to enter the London Flight Information Region; and then starting to accept traffic at about a third of the normal intensity once the radar came back in. By mid- afternoon the traffic backlog had been cleared. Aircraft which were already airborne within the region were either put into the hold, or in the charge of an airport radar, or of a radar centre like Manchester; or they were pro cedurally separated. There were no incidents. In less than six months LATCC will have a com pletely new electrical supply system which is "even safer" than the present one. But already it has been reviewed and will probably be modified in the light of what happened on November 15. For Sale Jt5 /TC /"1/CX JWTLCTLCL M.T.O.W.: 734,000 lbs./ 332,942 kgs. Engines: P&WJT9D-7A Interiors: 414/381 pax Galleys: Main deck Contact: C. Jeffrey Knittel Vice President Manufacturers Hanover 270 Park Avenue New York, NY 10017 Tel: (212) 286-6802 Telex: 421-790/420-966 555 MANUFACTURERS 00 HANOVER FLIGHT INTERNATIONAL, 20 December 1986 9
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
