The fuselage of a Dash 8 turboprop aircraft was penetrated in two places when a propeller blade collar separated shortly after take-off from Darwin.
The DHC-8-202 (Dash 8) aircraft had departed Darwin Airport for aerial work on 3 December 2019 when during the early stages of the climb, the flight crew heard a loud bang. Based on the observations by one crewmember the noise was assumed to be due to a birdstrike. With no issues with controllability and all systems functioning normally, the crew elected to continue the flight, which was undertaken without further incident.
On the ground, a subsequent engineering inspection found that the number 2 blade collar on the right propeller was missing and there was damage to the right propeller and ice shield on the right side of the aircraft fuselage. Removal of the shield revealed the fuselage had been penetrated in two places.
An ATSB investigation identified that the propeller blade collars on the number 2 and number 3 blades had previously undergone field repairs, after having been found loose. Examination of both blades showed evidence of inadequate cleaning and surface reparation on the number 2 blade shank, and that the collar on the number 3 blade was loose due to the presence of adhesive from the field repair.
"It is likely that surface preparation issues from the field repairs resulted in a lack of adhesion between the number 2 blade and its collar, leading to its separation in-flight," said ATSB Director Transport Safety Stuart Macleod.
"The blade collar then struck the number 1 blade, accelerating the fragments of the collar forcefully into the aircraft's fuselage."
"This investigation reminds operators and maintenance personnel that due to constraints on equipment, time, and experience, field repairs can be a source of added risk to an aircraft," said Mr Macleod.
"To minimise risk, maintenance manuals should be closely followed when conducting field repairs and operators should consider alternatives such as replacement over repair whenever practical."
In response to this incident, the aircraft operator, Cobham Aviation Services Australia, has released an engineering notice requiring the entire blade assembly to be replaced in the event of a loose or cracked blade collar and that if a serviceable blade assembly was not available, collars were to be replaced in consultation with a Technical Services Engineer, and in strict accordance with the component maintenance manual.
Mr Macleod noted that the incident also serves to remind pilots that damage to their aircraft may not always be apparent.
"This occurrence highlights that in‑flight damage may not always be readily apparent to flight crews, and in instances of abnormal noises and vibrations they should seriously consider terminating the flight," he said.
You can find here the investigation report AO-2019-074: Propeller blade collar failure involving de Havilland DHC-8, VH-ZZA, near Darwin, Northern Territory, on 3 December 2019
