ASN Wikibase Occurrence # 242857
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| Date: | Thursday 21 June 2007 |
| Time: | |
| Type: |  Bell 412 |
| Owner/operator: | Helicópteros del Sureste |
| Registration: | EC-HYM |
| MSN: | 33045 |
| Year of manufacture: | 1981 |
| Fatalities: | Fatalities: 0 / Occupants: 1 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Abanilla (Murcia) -
 Spain
|
| Phase: | Landing |
| Nature: | Fire fighting |
| Departure airport: | |
| Investigating agency: | CIAIAC |
| Confidence Rating: |  Accident investigation report completed and information captured |
The helicopter was taking part in efforts to extinguish a forest fire in the El Canton mountain range, located north of Mascivenda, within the municipal limit of Abanilla (Murcia). On board was the pilot, who was using a bambi bucket to perform the water drops. After releasing several loads, he left the bambi bucket on the ground near the fire. The terrain was irregularly shaped and slightly inclined The maintenance technician then boarded the helicopter and they proceeded to the base in Alcantarilla (Murcia) to refuel.
After refueling, they went back to pick up the bambi bucket and they landed. The mechanic exited and went to the front of the helicopter so as to hook up the bambi bucket. At that moment, while the aircraft was resting on the ground but with a certain amount of lift (the collective was not completely down and locked), it started to vibrate vertically.
The pilot stated that he decided to climb to try to eliminate the vibrations, but when they did not subside, he tried to land once again, moving laterally a distance of some 50 m across a terrain that was at about an 8° incline.
During this maneuver the blades of both rotors struck a tree and the helicopter fell to the ground with the nose facing to the northwest. As a consequence of the impact a fire broke out that affected part of the passenger cabin, though it was immediately extinguished using equipment available in the area.
The pilot was not injured and exited the aircraft under his own power.
There was significant damage to the main rotor, two blades of which (blue and yellow) were severely affected, the tail cone (the aft half of which detached), and the landing gear skids.
According to information provided by the AEMET, winds in the area were from the south at 14 kt, gusting up to 25 kt.
CONCLUSION
The cause of the accident is considered to be the appearance of vibrations that hampered control of the helicopter and degraded flight conditions, which forced the pilot to make an immediate landing, resulting in the helicopter impacting a tree.
The appearance of vertical vibrations could result from the simultaneous occurrence of three factors:
• The helicopter collective stick was not in the full down flat pitch position which may have allowed vibratory interactions between the main rotor and airframe.
• The loss of the mounts’ ability to absorb the vibrations transmitted by the turning rotor to the structure and resulting from the degraded mechanical characteristics of the assemblies, as evidenced by the cracks and corrosion present inside one of the components. Degradation in the static and dynamic spring rates of the mounts (softening) would lower the pylon roll mode frequency and into resonance or near
resonance with the main rotor 1/rev vibration.
• The previous landing on terrain with an irregular surface and inclined at an angle above that specified in the helicopter manual and in adverse wind conditions.
Accident investigation:
 |
|
Sources:
CIAIAC Ref. A-028/2007
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 24-Sep-2020 08:06 | ASN Update Bot | Added |
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