I was away for a month and now can hear and see passenger airplanes from my room in Sathorn, which has never happened before. Friends confirm and one checked online and found that all air traffic to/from Don Mueang airport DMK now goes south over Bankgok. Before it was all north. Why is that?

Wind.  Today they are back to normal.

I didn't notice any wind on ground, but of course higher up there might be wind.

Indeed, today I didn't see or hear any, contrary to yesterday. 

3 minutes ago, ChristianPFC said:

I didn't notice any wind on ground, but of course higher up there might be wind.

Indeed, today I didn't see or hear any, contrary to yesterday. 

 

Wind is from the NW, only 8 Kts.  Until today it has been stronger and from the NE.

31 minutes ago, ChristianPFC said:

I was away for a month and now can hear and see passenger airplanes from my room in Sathorn, which has never happened before. Friends confirm and one checked online and found that all air traffic to/from Don Mueang airport DMK now goes south over Bankgok. Before it was all north. Why is that?

Yeah, I had noticed planes flying over the city the last few days which was pretty cool. As @Upnotover said the answer is wind as they always want to land (and take off) into prevaling winds as it means they are landing with a lower ground speed whilst still maintaining the right ground speed. They get more lift at slower (ground) speeds which makes it much safer, the brakes have less work to do etc.

Suvarnabhumi changes direction regularly as the winds there change fairly frequently.

1 hour ago, ChristianPFC said:

I was away for a month and now can hear and see passenger airplanes from my room in Sathorn, which has never happened before. Friends confirm and one checked online and found that all air traffic to/from Don Mueang airport DMK now goes south over Bankgok. Before it was all north. Why is that?

 

Its happened before - you have simply not noticed it before. 

 

Bangkok’s prevailing winds are mostly from the north-east in the dry season (November–February) and from the south-west in the wet season (May–October).

 

DMK’s 03 / 21 runways point roughly NE-SW (28° / 208°).

BKK’s 01 / 19 runways point roughly NNE-SSW (14° / 194°).

 

 

You have simply 'noticed' aircraft flying into the 'seasonal' November-February winds from the North East - and hence the flight direct from the South / South West (i.e. over Sathorn)

I love the view when coming in from the South

20 hours ago, josephbloggs said:

Yeah, I had noticed planes flying over the city the last few days which was pretty cool. As @Upnotover said the answer is wind as they always want to land (and take off) into prevaling winds as it means they are landing with a lower ground speed whilst still maintaining the right ground speed. They get more lift at slower (ground) speeds which makes it much safer, the brakes have less work to do etc.

Suvarnabhumi changes direction regularly as the winds there change fairly frequently.

 

Landing with a bit of tailwind component can be preferable if it saves flight time. 

 

At Utapao, for instance, Bangkok Airways flights from the south quite often ask for RWY 36 even with a bit of tailwind because it saves a lot of time (and fuel) over being routed round to the north for approach to the reciprocal RWY 18. 

 

 

9 minutes ago, BKKBike09 said:

 

Landing with a bit of tailwind component can be preferable if it saves flight time. 

 

At Utapao, for instance, Bangkok Airways flights from the south quite often ask for RWY 36 even with a bit of tailwind because it saves a lot of time (and fuel) over being routed round to the north for approach to the reciprocal RWY 18. 

 

 

BS ... you don't want a tailwind when landing or taking off.  Stick to topics you might actually know something about 

20 hours ago, richard_smith237 said:

 

Its happened before - you have simply not noticed it before. 

 

Bangkok’s prevailing winds are mostly from the north-east in the dry season (November–February) and from the south-west in the wet season (May–October).

 

DMK’s 03 / 21 runways point roughly NE-SW (28° / 208°).

BKK’s 01 / 19 runways point roughly NNE-SSW (14° / 194°).

 

 

You have simply 'noticed' aircraft flying into the 'seasonal' November-February winds from the North East - and hence the flight direct from the South / South West (i.e. over Sathorn)

Today, as yesterday, we have planes landing at DMK from the North and at BKK from the South.  Both report 6kts 340deg wind. Guessing there must be some speed/direction calculation that dictates when a certain direction is needed?

Naively described: where does the cold spell come from?

China, winds from the north.

 

I remember more than once doing a time consuming loop over the sea to land at Suvarnabhumi from the south when coming domestically from the northeast.

That's definitely nothing new.

 

Just looked up: winds currently from NNW.

3 hours ago, KhunLA said:

BS ... you don't want a tailwind when landing or taking off.  Stick to topics you might actually know something about 

 

Right ... I'll ignore the many times I've heard Bangkok Airways flights coming into Utapao and asking Approach for 36 even though runway in use is 18. These are old charts but maybe you'll get the picture: if accepting a modest tailwind cuts out around 50+ track miles, that's a considerable saving in time at 230 kts or less and fuel (time and fuel burn at low altitude).

 

Coming from the South if you fly the RNP 36 approach >

 

 

Coming from the South if you have to fly the RNP 18 approach >