Stan Woolley #67, an interesting point, which is similar to many disparities in the industry. The problem might originate with:-
- The aircraft certification standard may be pre regulatory change - Older aircraft – ‘Grandfather Rights’. This could mean that the risks associated with landing differ from those in a modern aircraft.
Alternatively, the aircraft may be using a different standard of landing performance, or that the aircraft is not affected (unlikely).
- There might be disparity between certification and operational requirements, either within the manufacturers documentation, or the certification and/or operational regulations.
- Manufacturers and/or regulators might assume a landing distance additive is used in icing conditions, i.e. it’s the operator’s responsibility for compliance with (safety) regulations.
- There could be problems of communications; cf TAM, Spanair accidents, where ‘lost’ or corrupted operating information from manufacturer / regulator can contribute to an accident; – check for old notices to operators, advisory manual revisions, etc.
So it might not be surprising for manuals to have differing standards, but what is consistent is the operator’s responsibility for a safe operation, which comes down to the Captain’s responsibility on the day. Thus, it is important to understand all of the aspects which could affect the landing, the assumptions made in the regulations, and the risks involved. A good reference which covers normal operation is the UK AIC (#34) and also the relevant certification standards i.e. CS 25, FAR 25.