Learjet 35
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 50; Flight Crew Total 10600; Flight Crew Type 2500
Human-Machine Interface; Fatigue
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance; Ground Event / Encounter Object; Inflight Event / Encounter Object
Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Declared Emergency; General Maintenance Action
Aircraft; Human Factors; Procedure
I arrived at the hangar to reposition [the aircraft] for refueling followed by a maintenance test flight. The aircraft (A/C) was pulled out of the hangar and a preflight inspection was completed with no anomalies found except for the emergency air being on the low end of the green range (1900lbs). The A/C was taxied to where the refueling was preformed. Following refueling; the emergency air was serviced by maintenance personnel. Just prior to entering the A/C for the test flight my co-pilot performed a walk around with no anomalies found.Engine start and taxi to the active runway were uneventful. During takeoff with the co-pilot at the controls; approximately 3-5 seconds after rotation the right avionics cowl cover dislodged and was stuck perpendicular across both windows. I took the controls and instructed the co-pilot to declare an emergency and request landing on runway 7R. We decided to leave the A/C configuration as it was (flaps 8 gear down) and make a flaps 8 landing so as not to change the airflow over the cowl in case it were to depart the A/C further and damage either an engine or tail component. Once this decision was made we verified 'Flaps 8; Gear Down; 3 Green' and verified hydraulic pressure Followed by a Vref speeds to be flow for flaps 8 (Vref +20). The remainder of the approach and landing was made uneventfully. The cowling fell from the window just as we were coming to a stop on the runway. As the cowl slid off the left side window brakes we fully applied to avoid contact [by] the left main tires; however the A/C didn't stop in time and the cowl was run over by the left main. We continued our taxi into the ramp and the A/C was parked and secured followed by a phone call to Ops Control to advise of the situation.The mechanic that serviced the emergency air (located in the right avionics bay) stated that he had forgotten to tighten the fasteners for the right avionics cowl after removing it to service the emergency air. This individual had been on shift for 14 days straight and in my opinion made a mistake due to fatigue.
While departing on a maintenance test flight the flight crew of a LJ-35 experienced the loss of the right avionics cowling which was held against the windshield by the airflow until after landing when the aircraft slowed and it fell off and was run over by the left main wheels. The emergency airbrakes had been serviced via the missing cowling and the Mechanic had failed to secure the retention screws. Fatigue due to continuous shift duties by the Mechanic was cited as a contributing factor.