Friday, August 17, 2012

Crosswind Landings and A Surprise 35-knot Headwind


Malaysia is considered a mild climate country as there is no extreme temperature. Most of the time it lies between 28C to 33C in the afternoon with a drop of about 3C in the early morning in the lowlands where most people live. Similarly winds in Malaysia rarely reach above 20 knots, so pilots generally have little experience in handling strong crosswinds during landing. For mild crosswinds, some training in crabbing and sideslipping techniques for landing is usually made mandatory  .


In the former, the nose of the aircraft is deliberately pointed at an angle into the wind to counteract the otherwise sideways drift leewards. So, instead of pointing straight towards the runway, the aircraft is "crabbed" towards it. Moments before the wheels touch the runway, the nose is swung back to align with the centreline on the runway so that the wheels will roll forward as normal and not be dragged sideways causing the aircraft to skip or even topple on its side.

The latter technique involves lowering the windward wing while keeping the nose pointed straight towards the runway. The resulting sideways lift of the wings will counteract the otherwise leeward drift. The disadvantage of this technique is that the plane will sink faster towards the ground as the wings' vertical lift is now reduced by its sideways component which was created by banking the wings windward. The advantage of this technique, however, is that one can come in higher than normal and still be able to land on the threshold (a spot just after the edge of the runway marked with white stripes nicknamed "piano keys").

I have occasionally used both techniques over the course of my flying years but there was one instance when I could not use them and had to quickly devise my own technique. This was because this time the wind was coming from the front at about a 15-degree tangence  but the wind speed was 35 knots!


Here is how it all started. It was a bright day and I thought I would put in a half-hour to one-hour flight within the training area called R218. This area is a reasonably wide corridor that lies roughly between Kajang (2 minutes away from Sempang, our home airfield) and Semenyih. It has an upper limit of 2,500 feet and is used for training purposes as well as a transit lane for flights to and from the south. I scanned the sky before preflighting the aircraft and noted some rain clouds in the distance over Subang 6 miles away. They did not look threatening at all.

After obtaining Air Traffic Control (ATC) clearances, I took off and practised some manoeuvres within the training area. After about 30 minutes, ATC radioed me that the weather was closing in on the airfield and I was advised to return to base. As I neared Bukit Besi overlooking the airfield, there was a huge dark cloud hanging right on top of the runway and ATC advised that I was cleared to land with the surface wind indicating 200 degrees at 35 knots. Never had I heard such a strong wind from any ATC before but I believed it because that huge cumulonimbus cloud had a base at only around 2,000 feet. I could see the trees around the airfield swaying wildly. ATC then came on with a polite question "Do you need any assistance?" which they always say when they think a pilot or an aircraft might be in trouble.


I assessed the situation as I turned right to join downwind at 1,000 feet for a left-handed pattern for Runway 22. With the wind almost head on at 35 knots and my normal final approach speed at 60 knots, my airspeed would show 95 knots when I touch down but the ground speed would be just 60 knots. This could not be the usual landing using flaps anymore as the flap limiting speed is only 80 knots and an airspeed of 95 knots might just rip them off. A flapless approach at an airspeed of 105 knots (normal flapless approach is at 70 knots) would just do the job, so I told ATC "Final, no flaps" which he acknowledged. By that time the sky had opened up and heavy rain was pouring on the aircraft and the airfield. It was a totally new experience for me to see the Airspeed Indicator (ASI) showing more than 100 knots as I touched down smoothly without flaps. All my previous no-flap landings over the years had not more than 70 knots or thereabouts on the ASI, so it was hard to believe that I was doing what I did as I descended the last 300 feet onto the runway and rolled out. The arithmetic has once again been proven - 105 knots on the ASI with a 35-knot headwind is equal to a 70-knot landing.


I thanked the ATC as I taxied into the ramp and stopped the aircraft. Another problem had however just cropped up. There was no umbrella in the plane and there was no way I could run into the hangar without getting drenched to the skin. So I waited it out in the cockpit for about half an hour before the rain finally eased. By then the aircraft's wheels were totally submerged in water. I removed my shoes and socks, rolled up my pant legs and waded to the hangar. So much for the Malaysian weather, a short flight in a bright sky can turn into a freaking thunderstorm and flooding in less than 45 minutes.

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