Friday, 21 October 2005 00:57
Hello Captain Lim,
I have a question regarding Clear Air Turbulence.
I was recently traveling on a Boeing 737-800, en-route from Kiev to Amsterdam. The flight was going smoothly and had reached the cruising altitude when the cabin crew began serving the passengers. Suddenly, there was a loud bang and the plane jolted violently to the left and also seemed to lose altitude. Although there was initial panic, the incident lasted no more than 2-3 seconds and the pilot did not switch on the fasten seat belt signs. Being a bit worried at this point I opened my window blind as I honestly thought the engine had blown!
About a minute later, the captain reassuringly told us that we had passed through Clear Air Turbulence - probably caused by the jet stream from another aircraft ahead of us. The rest of the flight was uneventful and we landed safely in Amsterdam.
So, what exactly could have caused this? And would this be classified as severe or extreme? Or is it normal? In all my years of flying, this is the only time I have experienced real fear and would like to think that was a very rare occurrence!
What you have experienced was probably what your captain had said - to be exact, wake turbulence - a form of Clear Air Turbulence.
I just had a similar experience somewhere near the Bay of Bengal on my way to Zurich about a week ago. We were suddenly jostled by this turbulence and then I saw from my radar screen, another reciprocal Boeing 747-400 had passed us at 1000 feet above. This is the normal vertical separation when flying on RVSM (Reduced Vertical Separation Minima) rules. That wasn't the main issue but what I found out was that the wind was the problem. We had a tail wind and it had blown the wake turbulence downwards as the Boeing 747 flew passed us - hence the clear air "wake turbulence".
It does happen once in a while and this is the reason why I always remind my passengers to be secured with their seat belts whenever they are seated even though the seat belt signs are off. This is to preclude such an unforeseen event happening.
I would classify this as moderate to severe turbulence.
I wish you a safe and pleasant flight next.