Originally Posted by KACommuter

It does actually rain in Beijing in summer, and PEK is unable to handle it as it's dry the rest of the time. What KL-ites regard as normal heavy rain would be regarded as an uber-thunderstorm in Beijing, and their ATC can't cope.

The other issue is military exercises on the route which seem to be more frequent in summer presumably due to days being longer.

So HKG PEK in summer is not great at the best of times.