David Learmont: Bad weather the wildcard that all pilots learn to fear
Published 11/02/2011 | 05:00
FOR aviators and mariners alike, bad weather remains a hazard, and even the most advanced technology available today does not enable aeroplanes and ships to be operated as if the elements are of no consequence.
Storms, despite technology, remain powerful and dangerous, able to toss aeroplanes and ships around like corks.
Fog, like that at Cork Airport yesterday, brings the insidious risks with which motorists are familiar.
But whereas a driver can react to reduced visibility by slowing down or even stopping, an aeroplane seeking to land cannot do that.
Even the relatively small Fairchild Metroliner that crashed at Cork has to maintain a flying speed of more than 100mph until it has been safely planted on the runway by the pilots.
There are airliners that can carry out "blind" landings using autoland systems, but these include only large, hi-tech jets, and their advanced onboard equipment has to be matched by equally smart guidance equipment on the ground, which is so expensive to buy and maintain that it only makes commercial sense to install it at major international airports where poor visibility is a fairly high risk.
Cork Airport is not in that category, and neither is the Metroliner, a twin turbo-propeller aircraft with seats for 19 passengers.
Cork has a guidance system called an instrument landing system (ILS), which is the approach aid that the Metroliner pilots used, despite being able to see nothing but mist out of their windscreen, to guide them down the gentle glideslope toward the runway.
But at a predetermined point in the descent, known as the decision height, the pilots have to look up from their instruments and make a decision about whether they can see enough of the high intensity runway lights to be able to make their hand-flown, visually directed landing.
If they cannot see enough lights, they instantly increase engine power and climb away safely. The pilots at Cork did this twice.
First they approached Cork's southbound runway 17, and elected to abandon the attempt.
They continued flying south for a short time before making a U-turn to try an approach to the same runway, but landing in the opposite direction, hoping for better visibility.
But still the visibility was not good enough, and the crew abandoned their second attempt.
After climbing away the second time they had a decision to make; should they divert to another airport, or have another attempt? The weather at Shannon was much the same as at Cork, but Dublin would have been good enough according to the forecast.
When the Air Accident Investigation Unit is able to listen to the pilots' deliberations on the cockpit voice recorder, we will learn more about the reasons why they concluded that they should try a third time.
But the captain made what turned out to be the fatal decision to try once more, and intercepted the ILS beam for guidance toward runway 17, the southbound runway again. It can be very tempting to try, because the visibility in fog can vary from moment to moment.
There is still -- not surprisingly at this early stage -- a lot of mystery about what happened in the last few disastrous seconds of the approach.
At decision height, about 200ft above the level of the runway with about a mile yet to go to touchdown, the elapsed time from the decision to the landing is less than a minute.
The reported visibility at that time was 400m, which is marginal. If that report is accurate for the conditions on the approach, the pilots would not have been able to see the runway lights at decision height, but they might have been able to see some of the approach lights.
What happened in those last seconds that caused the aircraft to come to a halt upside down in the grass off the right-hand side of the runway?
The wind was light, so the aeroplane was not being tossed around in turbulence. Was there a technical problem, even minor, which distracted the pilots while they were trying to land?
If there was, they didn't tell air traffic controllers about it.
Did they push their luck by descending through the decision height and continuing the approach, hoping to get sight of enough runway lights to be able to land and deliver their passengers safely to their chosen destination?
Or could they actually see enough runway lights when they passed the decision height, but then entered a sudden and unexpected bank of thicker fog just as they were approaching touchdown? Fog can do that sort of thing, as drivers will know. Investigators will find out and report in due course.
Pilots do not take pot luck on how things will be at their destination airport.
Like other airline pilots, before they walked out to their aeroplane at Belfast City Airport these pilots would have checked detailed weather forecasts for Cork Airport.
They would also have checked the forecast weather at a number of other airports not far away and, on the basis of that, they would have designated their primary 'alternate' airport, and others to back that up.
Then they would have ensured the aircraft had enough fuel to carry out at least two attempts at landing at Cork followed by a diversion flight to one of the alternates.
As little as possible is left to chance, but despite today's technology, the natural elements will continue to test mankind in aviation and marine endeavours for the rest of time.
David Learmount is the operations and safety editor at Flightglobal (see www.flightglobal.com), and a former RAF flying instructor who flew Lockheed Hercules transport aircraft