Thanks for the replies! Appreciate it.
I was having a discussion with someone about Aeroperú Flight 603 - they crashed into the sea after taking off with the static ports still taped following maintenance work.
They had no idea about their altitude or airspeed, but I had two questions regarding that:
* Why they didn't trust or use the rad alt? GPWS was operational.
* Why they didn't decompress and use the cabin altitude indicator as an altimeter (from your responses it seem this would have worked).
I figured they could have used the IRS GS readout for approximate speed reference, allowing for the fact it accounts for wind.