Gentlemen,
we live with a conucopia of different certification procedures, 1 set for our aircraft certification (FAR25/JAR25), 1 for the procedures we fly (TERPS/Doc8168) and 1 for our airline operation (FAR/OPS1). These 3 sets of documents are by no means in complete alignment with eachother, but FAR/JAR25 is still regarded as sort of a baseline when designing the other sets of documents (no point in designing ops or procedures that no currently certified aircraft can fly
)
So, FAR/JAR25 must only be seen as a list of
minimum performance and information requirements (along with a long list of other requirements that do not pertain to this discussion). See it as a checklist that the FAA/JAA use when they are ceritifying the aircraft ("Hmmmnn, must be able to...
Can it do that
It can? Very good, checkmark, onto next item"
). It will
not give you any specific data as to weather or not it is legal or safe to operate into or out of any particular aerodrome - only tell you what the aircraft as a minimum must be able to achieve, even when operating out of a MSL/ISA aerodrome with terrain as flat as a pool table for the next 100 miles around.
TERPS/8168 tell us how the procedures are designed and flown. But - at least Doc8168 - starts off by telling us that "These procedures assume all engines operative"
This means that we
can in fact use tham as a kind of "poor mans" OEI performnace guideline. If your aircraft is able to meet the required climb gradient on the required track (both departure and MAP), then you can safely fly these tracks, adhering to your normal climb/speed schedule, as long as your net gradient does not fall below that required by the procedure.
Next, we look at FAR/OPS1. These documents also specify
minimum performance requirements, e.g. ability to climb & maintain 1500 ft. above departure AD. This is not to say that on any given day at any given aerodrome this is a particularily sound or safe place to be (INN, CNF, FAE and other european pearls spring to mind), but you must comply with this requirement, even when departing an aerodrome in completely flat surroundings). In addition, FAR/OPS1 establishes rules for by how much you must clear obstacles laterally, vertically and what obstacles to take into account, both for the missed approach and for departure. When we look at theese rules, the specify much lower clearances and take far fewer obstacles into accoundt than e.g. Doc8168. Therefore, if you only use the 8168 missed approach/climb requirement, you may be facing quite severe TOM/LM limitations, whereas looking at the same obstacle scenario for either missed approach or departure using the FAR/OPS1 methology and clearances, you might find yourself not being mass limited at all. More mass = more fare paying mass = revenue = everybody happy (except of course the flightcrew who now have to comply with a 2-page emergency turn procedure
)
When comparing Doc8168 missed approach/departure and OPS1 requirements, you may find that you can fulfill the OPS requirements using the Doc8168 missed approach track. If this is not the case, an emergency turn procedure must be established, different from the missed approach/SID track.
Hope this helps - brgds,
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