What offences may be committed under the Railways and Transport Safety Act by a master, a pilot or a seaman who is on duty?

Under section 78 of the RTSA, a professional master (at any time when he is on board), a professional pilot (when on board), or a professional seaman while on board on duty commits an offence if the proportion of alcohol in his breath, blood or urine exceeds the prescribed limit. These persons commit a separate offence if their ability to carry out their duties is impaired because of drink or drugs. ("Seaman" includes any officer below the rank of master.)