A four-engine air tanker, an L-188, struck a tree while making a retardant drop on a fire August 23, 2020. The tanker was working out of the retardant base at the Chico, California airport and landed safely with no injuries.
There was damage to the leading edge of the left outboard wing, lower outboard wing planks, left inboard flap leading and trailing edge, as well as scuff marks (but no damage) to the #1 prop. The pilots said they knew the drop was low, observed trees near wing level, but were not aware there was a tree strike until mechanics called the damage to their attention after they landed.
In 2019 an L-188 had to execute a belly landing when the crew was not able to get the landing gear down and locked. There were no injuries.
Below is the full text of the “Narrative” and “Corrective Action” sections as published on SAFECOM about the tree strike:
On bombing run on fire BTU Complex, aircraft entered smoke on short final, dropped load, and exiting the smoke observed trees near wing level. Aircraft climbed away with no indication to the pilots of any contact with trees. Aircraft then proceeded with a second run to drop remaining 50% load without incident, was released from the fire and returned to Chico. Flight crew had no indication of tree strike during flight. Evidence of tree strikes to the left wing discovered by maintenance during post flight inspection.
Aviation Safety Comments: This was the third drop of the day in the same area for this airtanker. The crew reported slowly deteriorating visibility for them in the area due to smoke. On this run an S2T airtanker dropped before them, and when the ATGS asked for them to tag-and-extend the crew stated that they could not see it from their position in the orbit. The ATGS then vectored them in for the drop. They successfully maneuvered onto the final leg and were cleared to drop.
Midway through the drop the airtanker briefly passed through a column of smoke, and when they emerged they immediately saw they were low. They quickly pulled up, stopped the drop, and returned to orbit altitude. They reported not to hear, see or feel any tree strike.
The ATGS had noticed the sudden pull-up maneuver and asked the crew if they were ok and if they had completed the drop. The crew stated all was ok and that they still had a half-load. Noting they were lower than intended on the previous drop, the captain opted to carry more power into the second drop, and conducted it with no issues. The ATGS then asked if they felt their visibility was continuing to deteriorate. Upon confirming it was, the ATGS opted to release them back to base. (Note: The ATGS continued to operate in the area with the S2T for a few more drops).
The crew landed back at base with no issues and left the aircraft. A short time after, they were called by maintenance back to the aircraft, which was the first time they were made aware of the tree strike. There was damage to the leading edge of the left outboard wing, lower outboard wing planks, left inboard flap leading and trailing edge, as well as scuff marks (but no damage) to the #1 prop.
Contributing Factors/Corrective Actions:
This crew is an experienced Canadian airtanker crew on their first day conducting aerial firefighting missions in California. A comment made by the captain was that his ‘muscle memory’ for power settings during drops had yet to account for the increased heat in CA. He realized after the low drop that that may have been a factor, and corrected by carrying more power into the subsequent drop, which he felt resulted in a normal height pass. This will be a talking point with subsequent Canadian crews that may come to California during this fire season.
Additionally, the aircraft Radar Altimeter appeared to not be functioning, which could have provided them with more situational awareness as they passed through the column of smoke on the drop. Before the aircraft is returned to service, the Radar Altimeter will be checked for functionality.
Lastly, a general sense during discussion with the crew is that they felt the smoke visibility in the area may have added an additional challenge as they acclimated to not only the environment, but also to CAL FIRE aerial firefighting operations (ex: FTA operations).
Additional training for visiting Canadian crews will be to emphasize that we not only hope that they feel comfortable in declining missions or drops they don’t feel can be conducted safely, we expect it.