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Compressor wash next after the engines have cooled down.

Is that a twin otter on a beach landing on one of the Scottish islands?

Cheap way to wash the lower fuselage!

A seaplane without floats :P

From Wiki (https://en.wikipedia.org/wiki/Barra_Airport):
Barra Airport (Scottish Gaelic: Port-adhair Bharraigh) (IATA: BRR, ICAO: EGPR) (also known as Barra Eoligarry Airport) is a short-runway airport (or STOLport) situated in the wide shallow bay of Traigh Mhòr at the northern tip of the island of Barra in the Outer Hebrides, Scotland. The airport is unique, being the only one in the world where scheduled flights use a tidal beach as the runway. The airport is operated by Highlands and Islands Airports Limited, which owns most of the regional airports in mainland Scotland and the outlying islands. Barra Airport opened in 1936. The airports only destination is Glasgow.

Hmm. Prop wash.