I'm a flight attendent for Singapore Airlines so I can tell you this.
For males, SIA only employs Singapore citizens or Singapore Permanent Residents.
For females, we do employ Singaporeans, Malaysians, Japanese, Indonesians, Indians, Chinese and Koreans.
The girl that one of the poster mentioned, I've got a strong feeling she's Junita Simon's sister from the description given. I can't remember her name though. Junita Simon is a model in Singapore. Their father, Anil Simon is a inflight supervisor with SIA as well.
SIA do employ part-Asians who are Singapore citizens or permanent residents. As Singapore is a multi-racial country, we've got many mixed marriages here. The most important thing they look out for when employing people of mixed parentage is that they must still look Asian and their slang should preferably be not too strong.
Hope this helps!