Schiphol airliner crash blamed on altimeter failure, pilot error - Wikinews, the free news source
This accident was blamed on altimeter failure leading to a CFIT because the autopilot believed the faulty altimeter and the crew noticed too late to intervene. The aircraft had a history of altimeter failure that had not been picked up.
My take on this emergency (it is a Mayday IMHO) would be to separate the aircraft laterally and get a shepherd aircraft (probably a friendly military crew, as they are used to flying in formation and will not have company issues to worry about) on him PDQ, whatever the flight conditions, then use the shepherd to escort him down the nearest ILS/PAR.