Arbroath's all-weather lifeboat has been taken out of service while the RNLI investigates a "serious" incident.
The RNLI said it had launched the probe at Arbroath Lifeboat Station after receiving a complaint, but would not release further details.
It said "some" crew members at the station have been stood down while the investigation is carried out.
The inshore lifeboat remains in service and all-weather cover is being provided by Montrose and Broughty Ferry.
A RNLI spokesman said the Institution would "not tolerate any behaviour that brings the work of the RNLI and our people into disrepute".
He added: "We are currently undertaking an investigation at Arbroath Lifeboat Station following a complaint about a serious incident.
"We won't be in a position to comment on the details of the incident until the investigation has reached a conclusion.
"However, some crew members have been temporarily stood down while the investigation is being carried out.
"As a result the all-weather lifeboat is currently off service due to the lack of availability of operational crew."
The spokesman said the RNLI would never consider taking a lifeboat off service "unless there was due cause and reason," and that they were working to get the all-weather lifeboat back in service as soon as possible.