It's been done before. From the excellent article "The Turn":
> Pilots, too, have relied on pendulums. It is said that an airliner inbound to New York in the 1950s lost all its gyroscopes in heavy weather over Block Island. The captain was a wise old man who had risen with the airlines from the earliest airmail days and was approaching retirement. A lesser pilot might have fallen for the trap of intuition. But the captain simply took out his pocket watch, dangled it from its chain, and began to swing it toward the instrument panel. Flying by the pendulum and the compass, he proceeded the length of Long Island in the clouds. After breaking into the clear near the airport, he landed and wished his passengers a good day.
But in this case the pilots didn't even need to do that. Their gyros were working correctly, so they had an artificial horizon right in front of them. The attitude of the plane was known. They even recovered their airspeed indicator after 30s (the second one after a minute)! All that was needed was for the pilot to stop pulling on the stick…
> Pilots, too, have relied on pendulums. It is said that an airliner inbound to New York in the 1950s lost all its gyroscopes in heavy weather over Block Island. The captain was a wise old man who had risen with the airlines from the earliest airmail days and was approaching retirement. A lesser pilot might have fallen for the trap of intuition. But the captain simply took out his pocket watch, dangled it from its chain, and began to swing it toward the instrument panel. Flying by the pendulum and the compass, he proceeded the length of Long Island in the clouds. After breaking into the clear near the airport, he landed and wished his passengers a good day.
(the entire article is really worth reading: http://www.theatlantic.com/past/docs/unbound/langew/turn.htm)
But in this case the pilots didn't even need to do that. Their gyros were working correctly, so they had an artificial horizon right in front of them. The attitude of the plane was known. They even recovered their airspeed indicator after 30s (the second one after a minute)! All that was needed was for the pilot to stop pulling on the stick…