As with all airline policies, YMMV. The answer depends on airline and/or individual check-in agent/station manager. I've had agents from one airline not allow check-in/boarding to Singapore with a US passport under 6 months validity while another airline did.
If you want to play it safe, go to US embassy/consulate and get a emergency passport. It's issued in a couple of hours, cost the same as a 10-year passport, issued with 1 year validity which you can trade it by mail back in the US for the 10-year without additional fee.