Hello Captain Lim
I am writing from Singapore. I noticed sometimes the plane takes off in one direction and sometimes in the opposite direction at the Changi Airport.
Why is that so??
SK Chee
Hi Chee,
For safety and performance reasons, airplanes should take off into wind. When wind direction changes, the ATC (air traffic controller) would have to change the runway in use.
For a more detailed answer about wind and flying, I reproduce an article, ‘The Good, the Bad and the Ugly Winds’ (also mentioned in my book LIFE IN THE SKIES) which I wrote in the in-flight Travel 3Sixty Magazine below…
The Good Wind
Ever wonder why you sometimes arrive at your destination from a flight earlier than you expect? It’s usually a pleasant surprise especially if your special welcoming-home party is not there for you yet! Well, the reason for this is that the good wind has been blowing your plane from the back. This is what we call a strong tail wind – a boost as if someone is pushing your back to make you move faster.
Wind can be good, bad or ugly depending on how it is perceived in relation to the plane. Wind is good when it helps to speed up the plane on a long journey but bad when it is blowing the plane from the back during a landing. Tailwind can cause landing distance to be longer, thus reducing the safety margin. Sometimes, it may even cause the plane to have a tail strike – literally causing its bottom to scrape the runway! Similarly, it is good when the wind is blowing from the front on take-off or landing and hence a shorter runway is required; but bad on a long flight as it takes a longer time to reach your destination.
On take-off, a strong headwind gets the plane airborne faster as compared to a tail wind. As such, the air traffic controller will use a runway with the strongest headwind. Consequently, some delays are expected when there is a need to change the runway as the wind direction moves for safety reason. Therefore all planes have to be re-sequenced either on the ground or in the air.
Crosswind Landings
Wind can be ugly when it blows across the runway at speed beyond the limitations as imposed by the manufacturer. This is known as the crosswind. For instance, on an Airbus A330, when any wind is more than 40 knots (depends on airlines); landing is not allowed on a dry runway. If the runway is wet, the crosswind is further reduced to 27 knots as it is more difficult to keep the plane centre on a slippery runway.
On 22 Aug 1999, a China Airlines MD-11 flight to Hong Kong crashed because of strong crosswind. Strong crosswind landings may be a little difficult as the nose is pointed to the wind direction in order to maintain the centreline of the runway. It looks awkward as the plane has to ‘crab-in’ and only points the nose back to the runway centreline just before touching down.
In this accident, the captain landed hard on the right landing gear because of the strong crosswind. As a result, the right engine scraped the runway resulting in the right main landing gear and the wing on that side breaking off. The plane then rolled inverted as it skidded off the runway.
There are lessons to be learned by the pilots – never land or take off on a runway when the crosswind is beyond the manufacturer’s recommended limitations. This reminds me of my own experience on a Boeing 777 flight from a previous airline. See The Divine Wind, October 2010 issue of the Travel 3Sixty magazine – an anecdote worth repeating and is reproduced below for those who missed the article.
Tryst with a Typhoon
I remember vividly an incident some years back in Shanghai when I was working for my former airline. I refused to take off on a Boeing 777 because of an approaching typhoon. An irate passenger on my flight said something to the effect of, “How come the other foreign Boeing 777 pilot, flying the same aircraft from another airline was able to take off whilst this cowardly pilot refuses?” This remark prompted the airport manager to try and persuade me to take off. I however was adamant and told him, “No way, my friend!”
Naturally, I too was surprised that the Boeing 777 which was parked next to us took off. Of course, this angered the passengers who had been stranded at the lounge for several hours. It made plain sense to the passengers if the other flight could take off, then why was this pilot (yours truly), being difficult.
I had my reasons and good ones they were too. You see, an approaching typhoon comes with winds which gradually increases in strength. More so, the wind on that day was blowing across the runway. Every plane has a crosswind limitation whereby the manufacturer cannot guarantee a safe take off if it exceeds a particular strength. The wind on that fateful day was gusting well above the take-off limit, and hence my refusal to take-off and endanger the lives of those in my care.
No Way José!
I tried my best to explain the reasons for my refusal to take off to the manager. He was not convinced at all. However, that all changed when we overheard on the radio that a United Airlines Boeing 747 and a Virgin Atlantic Airbus A340 were forced to return after aborting their departures.
I was pleased that I had stood firm in refusing to give in to the demands of the airlines airport manager. My passengers’ safety was of utmost importance and I was certainly not about to take a chance with it. I recalled a doctor’s comment once about my responsibility being heavier than his. He remarked that when a doctor makes a mistake, only one patient dies, whereas a pilot’s mistake would impact the lives of over 300 passengers!
The other pilot may have been trying to be heroic but each time we pilots sign in to fly an aircraft; we are duty bound, morally and professionally, to operate the plane as safely as possible. In all honesty in this instance, I’d rather be a coward who’s alive (along with all his passengers!) than a dead hero.
Wind shears
A report alleged that wind shear was the probable cause of a Boeing 737 crashing into the sea at the Bali International Airport recently. Fortunately, all 101 passengers and 7 crew survived the crash when the plane broke apart on the shallow water.
Severe wind shear can be very vicious. It is caused by a sudden and powerful change in wind direction that occurs frequently in or near thunderstorms. The downdraft created would give rise to a strong headwind that will cause a corresponding increase in airspeed. When the plane passes through the downdraft, it would encounter a tailwind, which will cause the aircraft to lose airspeed and altitude dangerously.
Airplanes are most vulnerable to wind shear during take-offs and landings. As such, wind shears can turn very ugly when caught unexpected. It has also caused the following three crashes below:-
On June 24, 1975, an Eastern Air Lines Boeing 727 crashed whilst landing at the JF Kennedy International Airport in New York due to severe wind shear caused by the thunderstorms. Of the 124 people on board, 106 passengers and 6 crew members did not make it. The investigation board found that the captain was aware of severe wind shear reports on the approach path but decided to continue nonetheless. That was a fatal decision!
On August 7, 1975, a Continental Air Lines Boeing 727 crashed after take-off from the International Airport at Denver, Colorado due to severe wind shear. 134 persons aboard the aircraft survived the crash; 15 persons were injured seriously. The aircraft was badly damaged.
On 3 July 1982 a Pan Am Boeing 727 flight crashed on take-off after encountering wind shear. The aircraft was destroyed during the impact and subsequent ground fire with many fatalities.
Predictive Wind Shear System
Lest all these accidents worry you, improvement in technology has come to the rescue! Human beings are very innovative. Lessons from past incidents have always helped to make flying safer for the future!
Today wind shear detection technology has been developed to enable pilot to predict wind shear even before take-off. Most modern planes including planes such as the Airbus A320 and Airbus A330/A340 are now installed with this system.
Basically this warning system makes use of the weather radar to identify the existence of wind shears ahead before take-off. The radar picks up water and ice particles ahead of the airplane and warns the pilot with this audio message “Wind Shear Ahead!” This is effective and provides the pilot an opportunity to abort the take-off.
Whilst airborne, during take-off or landing, this similar system also warns of any wind shear ahead. It is not clear whether the wind shear warning was activated in the above B737 accident. In my flying career since the installation of this warning system, I must admit that I have only encountered a real “Go Around, Wind Shear Ahead!” warning once during my approach to land. I did what I was taught – abort the landing and returned for another safe one when the gusty wind conditions subsided.
Conclusion
The next time you watch a plane landing cocked (pointing) towards the wind and not on the runway centre line, you know that the captain is working very hard to control a cross wind landing. He has to do that (‘crabbing’) or else he misses aligning on the runway centre line! Not to worry, just before touch down, he would use the rudder to bring the plane towards the centre.
Intensive wind shear practices by pilots in the airline constitute the mandatory six-monthly check to ensure that safer flights are carried out in the skies.
With that in mind, I hope to relieve any anxieties that you may have as a result of gusty winds during your flight.
Monday, 04 May 2015 15:47