Scandinavian Airlines System Flight 1209: Landing Gear Failure Analysis
On September 9, 2007, a domestic flight operated by Scandinavian Airlines System (SAS) experienced a critical mechanical failure that led to a dramatic emergency landing. The aircraft, a Bombardier Dash 8 Q400 registered as LN-RDK, was traveling from Copenhagen Airport in Denmark to Aalborg Airport when the crew discovered a malfunction in the landing gear system.
As the aircraft prepared for arrival, the flight crew attempted to lower the landing gear. However, the cockpit indicators revealed a problem: while two lights turned green, one remained red, signaling that the right main landing gear had failed to lock into position. The crew aborted the initial landing attempt and circled for one hour, attempting to resolve the issue and preparing the cabin for an emergency touchdown.
Upon touchdown, the right landing gear collapsed, causing the right wing to strike the ground. This impact triggered a fire, which was extinguished before the aircraft came to a complete stop. All passengers and crew were successfully evacuated. Five individuals sustained minor injuries, some caused by the evacuation process and others resulting from propeller fragments entering the cabin.
[ไม่มีภาพประกอบ]Key Facts
- Aircraft: Bombardier Dash 8 Q400 (Registration: LN-RDK)
- Date: September 9, 2007
- Route: Copenhagen Airport to Aalborg Airport
- Primary Failure: Right main landing gear failed to lock
- Casualties: Five minor injuries; no fatalities
- Root Cause: Galvanic corrosion of the hydraulic actuator eyebolt
Investigation into the Mechanical Failure
Following the incident, investigators focused on why the landing gear failed to deploy despite the crew's efforts, including unsuccessful attempts to lower the gear manually. The technical investigation revealed that the hydraulic actuator eyebolt—a critical component used to move the gear into place—had broken away from the actuator.
Detailed analysis of the actuator showed significant corrosion on the threads of both the piston rod (internal threads) and the rod end (external threads). This corrosion compromised the mechanical strength of the component, leading to its eventual failure during the landing sequence.
The Role of Maintenance and Cleaning
The accident drew intense scrutiny toward SAS maintenance procedures. At the time, Swedish authorities had recently criticized the airline following a separate incident where a Q400 engine accelerated unexpectedly during landing. While there were accusations that the airline had cut corners, the official investigation concluded that the failure was not due to a lack of maintenance, but rather over-cleaning.
Investigators found that the use of high-pressure washers during cleaning had stripped away the corrosion-preventative coatings between the eyebolt and the actuator rod end, leaving the metal exposed to the elements.
Scientific Cause: Galvanic Corrosion
AIB Denmark (Havarikommissionen) identified a metallurgical contributing factor known as galvanic corrosion. This occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte (such as moisture), causing the less noble metal to corrode faster.
In this case, the interaction between the nobler martensitic stainless steel and the less noble 4340 steel material accelerated the corrosion process. The damage was most severe where the piston rod threads were in direct engagement with the rod end threads.
Flight 1209 Summary Table
| Category | Details |
|---|---|
| Aircraft Model | Bombardier Dash 8 Q400 |
| Failure Point | Right main landing gear hydraulic actuator |
| Primary Cause | Thread corrosion leading to eyebolt failure |
| Contributing Factor | Pressure washing removing protective coatings |
| Metallurgical Issue | Galvanic action between stainless steel and 4340 steel |
Frequently Asked Questions
What caused the landing gear to collapse on Flight 1209?
The collapse was caused by the failure of the right main gear hydraulic actuator eyebolt, which broke away due to severe corrosion of the threads on the piston rod and rod end.
Were there any fatalities during the accident?
No, there were no fatalities. All passengers and crew were evacuated, though five people suffered minor injuries.
How did cleaning the aircraft contribute to the crash?
The use of pressure washers during maintenance removed the essential corrosion-preventative coatings, which exposed the metal components to moisture and accelerated the degradation of the actuator.
What is galvanic corrosion in the context of this flight?
Galvanic corrosion occurred because the actuator used two different alloys—martensitic stainless steel and 4340 steel. The interaction between these two different metals enhanced the corrosion process where they were in direct contact.
Did the crew attempt to fix the gear before landing?
Yes, the crew circled for one hour and attempted to lower the landing gear manually before deciding to proceed with an emergency landing.