Learjet 35
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor
Flight Crew Last 90 Days 88; Flight Crew Total 3400; Flight Crew Type 1353
Distraction
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance
Aircraft; Human Factors; Weather
We were descending for landing at IAH on the ROKIT1 arrival. Approach Control had advised to expect the ILS to 27; but said the Tower may offer 15R. We were cleared down to 3;000 FT. Approach asked if we had the field about 10 miles out at 10 o'clock; but neither of us could see any runway lights nor the beacon. We were still on the arrival route so the field was not directly in front of us. Approach again asked if we had the field at 8 miles out and cleared us down to 2;000 FT. The pilot not flying set 2;000 FT in the pre-selector and I initiated the descent using the autopilot. We told the Controller our windshield was somewhat fogged up and that neither of us could see the field. We were handed off to the Tower at some point and I'm not sure when in the event it was as I was focused on finding the field. Tower offered us 15R but we still could not find the field. I looked back to our instruments and realized that the autopilot had not captured the 2;000 FT altitude in the pre-selector which happens occasionally and we know to verify the capture. I missed it because I was so intent on finding the field. At approximately 1;400 FT MSL I applied power; disconnected the Autopilot; and climbed back to 2;000 FT. The Controller said he showed us low and reminded us we were assigned 2;000 FT and we acknowledged we were already correcting. We passed the last fix on the arrival and were just continuing on present heading when we acquired 15R. We were too close to make a visual approach so we requested vectors to the 27 ILS and the pilot not flying put that back in the FMS. We were vectored onto the approach and landed uneventfully.
Lear 35 First Officer descending to 2;000 FT on autopilot discovers at 1;400 FT that the autopilot has not captured the altitude and corrects.