Flight Sequence
The aircraft departed Cuatro Vientos Airport at 11:00 local for a local instructional flight with an instructor and a student pilot. After returning and lowering the landing gear, the crew noted that the nose gear did not indicate down and locked. They left the traffic pattern to attempt further gear extension procedures, including both normal and emergency extension, without success. Returning to the airport, they performed a low pass so that the tower could observe the gear position. The tower reported that the nose gear was retracted and its doors were barely open. After declaring an emergency, the crew landed on the main landing gear on runway 28. Both occupants were uninjured and exited the aircraft unassisted. The aircraft sustained damage to both engines and propellers, and the lower forward fuselage including the nose gear doors and their actuating mechanism.
Aircraft Inspection
With the aircraft at rest, the nose was lifted, and after manually separating the doors (without disconnecting actuating rods), the nose gear extended and locked properly. The main gear were down and locked. The doors appeared to have contacted the ground while nearly closed, with actuating rods slightly bent but no damage to their ends or hinges. No evidence of hydraulic system failure was found; fluid level was correct and no leaks observed. Subsequent cycles of gear operation (without doors) functioned correctly.
Maintenance Background
The last 50-hour inspection, performed on 17 April 2006, included checking shock absorbers, tire pressure, and lubrication of points specified in the lubrication chart. The 100-hour inspection on 17 March 2006 included retraction/extension cycles and door gap checks. After that inspection, a 20-minute test flight was conducted. The aircraft then flew 29 flights (44 hours, 55 landings) without reported gear issues. In the seven days before the incident, only two flights (2h50m, two landings) were made.
Landing Gear System
The gear is extended and retracted by hydraulic actuators powered by a reversible electric motor. All three actuators receive pressure simultaneously. The gear is held retracted by continuous actuator pressure; in the extended position, overcenter mechanisms and spring-loaded hooks lock the gear. Emergency extension releases hydraulic pressure, allowing gravity and airflow to extend and lock the gear. The nose gear has two continuous-hinge doors operated by a complex linkage actuated by the nose gear strut itself. When the gear retracts, it contacts a door mechanism piece, closing the doors and loading a spring that opens them when the gear extends. With the gear up, the doors are held closed by the strut's action, with no separate locking device.
Analysis
Based on tower observations and door damage, the doors were closed at the time of the incident. The nose gear and door mechanisms are largely independent. The hydraulic system appeared functional because the main gear extended and locked normally. When the doors were manually opened after the incident, the nose gear fell and locked, confirming the emergency system worked and the gear mechanism (excluding doors) was functional. The problem was therefore confined to the door blockage. Although the spring may not have been strong enough to open the doors, the weight of the gear alone might have opened them if only slightly blocked, especially with a brisk maneuver. However, the damage to the doors and mechanism after ground impact altered their condition sufficiently to preclude determining their pre-incident state and thus the exact cause of the blockage.
Probable Cause
The incident was caused by a blockage of the nose gear doors due to undetermined reasons.