We indeed know of at least one case (LAPA), but possibly one or two more that weren't properly investigated, where that happened.
Also, please note that the MD-82 that suffered the accident wasn't in "air mode" strictly speaking.
Most of the indications for "air mode" come from the front wheel sensor, others from the back. But even the ones in the front are divided between the left and right "wheel". Each of those sensors feed between half-a-dozen and a dozen relays, which in turn feed the "correct state signal" to between 1 and 4 devices each.
The Spanair MD-82 probably had only one of those almost 20 front wheel logic electrical relays fail, one that ultimately only affected two devices: the RAT probe heater and the take off configuration alarm (the other two devices connected were redundantly serviced by the right wheel circuit). So only the TOWS and the RAT probe heater thought they were "on the air". The rest of the airplane thought it was "on the ground". The absolute only signs that the airplane had any failures whatsoever would've been: a RAT probe heater turned-on while on the ground and a TOWS that wouldn't have responded with sound to a bad configuration takeoff check. If none of those symptoms were noticed, nothing would've seemed wrong at all with the airplane, which otherwise was, of course, perfectly fit to fly.
It was almost out of luck that the pilots noticed the RAT heater on while on the ground, giving them and maintenance the only chance to figure something was wrong at all. But they missed that chance. Also, if a mandatory TOWS check would've been included in the checklists (and actually performed by the crew), the failure would've also been noticed. But unfortunately the whole RAT issue was pbbly also the "spark" that made them distracted and rushed and finally triggered the oversight on setting flaps and the tragedy.
The MAP MD-83 in Lanzarote had the whole set of relays from the left front wheel "disconnected" by a pulled circuit breaker. And still, because most of those devices are actually ventilation/air conditioning/etc and a good number are redundantly serviced by the right wheel circuit, the pilots still didn't notice the "air mode" logic that affected probably a dozen or so non-redundant devices. They forgot to set the flaps/slats as well and took-off with an effectively disconnected (but perfectly serviceable) configuration warning alarm, so they didn't realize anything was wrong until the airplane started to stall.
Last edited by justme69; 23rd Oct 2008 at 12:06.