Dear Akhan
It's an adult Crested serpent eagle. It is a local eagle which frequents forested areas. It usually
makes repeated four-note calls while soaring in the sky. It is a whistle resembling 'fuf-fuf, vua-vua' in standard English pronuciation, short, low and flat pitched for the first two and in rising tone for the last two which are light and clear.
Last words,nice photos.
S L Tai