By now all reports/studies on noise abatement at Brussels Airport count thousands of pages and have become the subject of a political debate between the Belgian communities. In 2013 BeCA and the Flight Safety Managers of all all Belgian operators met at the office of the Federal Minister of Transport, explaining that a 12kt (7kt+5kt gusts) tailwind limit was NOT acceptable while most aircraft manufacturers specify a 10kt maximum.
This shows that safety is no longer the prime objective of this discussion.
Why do airplanes need to land into the wind?
When an airplane flies it has a certain speed compared to the air, so called air speed. Actually this is why the aircraft flies. The speed causes a relative wind to flow over the wings generating lift, an upward force which counteracts gravity. In still air, the air speed is equal to the speed the aircraft has relative to the ground. But if the air moves (we call this wind) the ground speed will either become larger (tail wind) or smaller (head wind). Because runways have a limited length and airplanes also have limited brakning capacity, you want to move as slow as possible relative to the ground (i.e. have a low ground speed) in order not to overshoot the concrete.
Another effect of tailwind during approach is the fact that planes are more difficult to stabilise. Normally pilots fly on a 3 degree glide path. If the aircrafts air speed is fixed, adding tail wind will increase the rate of descent to keep the same angle. In other words: if the rate of horizontal distance (ground speed) over time increases, then the rate of vertical distance over time must increase as well. All airlines have a policy for aircraft stabilisation. They say at what height above the ground (runway) an airplane should be in level-flight, at the correct speed with gear and flaps down - ready to land. Tail wind makes a pilot life needlessly complex.
This is way all relevant documentation tells you to avoid landing with tail wind.
- European Action Plan For Prevention of Runway Excusions (EAPPRE)
- Approach and Landing Accident Reduction (ALAR) Toolkit
- Manufacturer Flight Operating Manual (FCOM/FOM)
- Aircraft Operator Manuals (OM-A)
Currently all existing regulations are based on surface wind measurements. However the wind conditions on ground can vary significantly compare to the winds (direction and speed) at altitude. We strongly argue for a more comprehensive set of rules taking into account the winds aloft. A couple of years ago a co-operaion between Belgocontrol and Brussels Airlines investigated the option to send wind data in real time to the ATC controller through the MODE S capability of the transponder. Why don't we explore this further and add the gathered data to the discussion. Let's look at the numbers.
What does BeCA do?
BeCA has been and will be a strong advocate of flight safety. We understand that the political situation in Belgium is not easy, but when safety becomes subordinate to political interest, we need to ring the alarm bell. Let's look at the numbers. Let's do the math. Let's not try to re-invent the wheel. There is plenty of well-founded research available, and they all point in the same direction: stop tailwind landings.