KOLKATA: Over the past fortnight, over a dozen incoming flights to Kolkata have abandoned approach and pulled out at the last minute. In each instance, the pilot complained of malfunction in a critical visual landing guidance system installed at the southern end of the secondary runway. But with airport authorities insisting all is well despite a flurry of complaints, directorate general of civil aviation (DGCA) has asked Airports Authority of India (AAI) to get the precision approach path indicator (PAPI) recalibrated.
According to sources, the problem surfaced around two weeks ago when the primary runway was shut down for routine maintenance work. The pilot of a private airline, who was directed to approach the secondary runway from the south, veered away after the readings on the distance measuring equipment (DME) failed to match the indicators on PAPI. While DME tells pilot the distance between the aircraft and the runway, PAPI is a visual reference for the pilot to know the position of the aircraft relative to the guideslope or descent coordinate of the runway.
"Initially, all seemed normal when the pilot aligned the aircraft to the runway and began making a descent. A controller was in constant touch with him over VHF radio as the secondary landing strip does not have instrument landing system that allows pilots flying modern aircraft to simply lock on to the fly-by-wire system during the final approach and sit back while the plane lands automatically. When he was a minute away from touchdown, the pilot said exclaimed the PAPI showed he was flying lower than the desired altitude in the guideslope and would fall short of the runway if he continued the descent. He then pulled away from the landing procedure. When the controller asked him to go around and make a fresh approach in case there was a mistake, the pilot refused, saying the problem was either in the DME or PAPI alignment and that he did not feel confident to land on the secondary runway. We had no option but to stop repair work on the primary runway and clear it for the plane to land," a source said.
When other pilots also reported similar aberration in PAPI, the ATC shifted operations to the primary runway, shutting the secondary landing strip. While all landing strips have PAPI, the instrument becomes even more critical when there is no ILS.
A glitch in PAPI can lead to a faulty approach that can be a big risk and even cause an aircraft to crash. The PAPI itself consists of a light array positioned beside the runway. Comprising four equi-spaced light units colour coded to provide visual indication, the pilot knows he is on the right path when he spots two white lights on the inside and two red lights on the outside. When he sees four red lights, it indicates that the aircraft is lower than the desired altitude and will fall short of the runway . Four white lights indicate he is higher than the desired altitude.
When he views four white lights, it indicates that he is higher than the desired altitude and will overshoot the runway.
Though the pilots have had no problem approaching the secondary runway from north, a strong northerly wind during winter months forces operations to move to the south to avoid a strong tailwind.
Realizing the alignment of PAPI had gone haywire, perhaps during the runway's extension work, ATC officials asked AAI to check the lights and rectify the problem. The latter claims it got PAPI checked by airfield management and communication, navigation and surveillance (CNS) staff but found nothing wrong with the crucial instrument. Yet, the problem recurred when the primary runway was shut down the next time. It happened on November 7 and again on November 9.
"We know there is a problem but the airport will not acknowledge it. Unless PAPI is recalibrated, we will not use the secondary runway," a pilot said. Pilots of other airlines, too, said they would not risk landing on the secondary runway at present.
Sensing that operations at Kolkata airport may have to be shut down if the primary runway is not available, DGCA had asked AAI to get its aircraft to calibrate PAPI and fix the situation. Sources said the aircraft had been requisitioned and could arrive anytime next week.
http://timesofindia.indiatimes.com
Subscribe to:
Post Comments (Atom)
No comments:
Post a Comment