Re: "almost always mechanical backup for critical ... components."
Me: "incidents ... where passenger aircraft have been steered largely or solely by means of adjusting engine thrust "
Vic: "Feel free to post references to prove me wrong, but I doubt you'll find any.."
Is there a prize? :) A virtual pint will do, cheers.
http://en.wikipedia.org/wiki/Flight_with_disabled_controls (multiple incidents, well referenced)
Controls damaged by explosive device/weapons
Philippine Airlines Flight 434, a Boeing 747, on 11 December 1994. The hydraulics were damaged by a bomb in the passenger cabin.
DHL shootdown incident in Baghdad on 22 November 2003. The Airbus A300 DHL aircraft, hit by a surface-to-air missile, was the first jet airliner to land safely without any hydraulics using only engine controls.
Controls damaged by pilot error
Pan Am Flight 845, a Boeing 747, on 30 July 1971. When taking off from San Francisco International Airport, the plane struck the approach lighting system after taxiing onto a much too short runway. After the impact, the plane continued into the takeoff roll, though its fuselage, landing gear, and 3 out of 4 hydraulic systems were badly damaged. After making a full circle over the Pacific Ocean for an hour and 42 minutes and dumping fuel, the plane made a hard emergency landing at San Francisco, ending on its tail. All 218 passengers survived with just a few minor injuries.
Not surprisingly, there are plenty other examples with less satisfactory outcomes. As there are with engine failures. Not every captain could do what Sullenberger did when his engines stopped working. He unavoidably flew into Canada Geese. Perhaps surprisingly, engines aren't (weren't?) designed to be resistant to birds the size of Canada Geese.