zonnair: Excellent questions!
Many TREs differ in opinion, and some CAAs as well (evidenced by approved OM-As).
Here's what an Airbus' produced, EU-OPS compliant, OM-A sample says:
Reference: UG1100187 REV 07 / AIRBUS OPERATING PROCEDURES / ALL WEATHER OPERATIONS
8.4.5.3. LVTO with RVR between 150m and 125m (APPENDIX 1 TO EU-OPS 1.430)
EU-OPS has provision to further reduce the minimum RVR provided the Airline has obtained an operational approval to conduct LVTO with these minima. Among the conditions, which must be met, the visual segment is related to the aircraft type. A minimu visual segment of 90 m is required from the cockpit during takeoff run with the minimum RVR.
The visual segments for RVR 125m are given in the table below for each Airbus model:
AIRBUS MODEL VISUAL SEGMENT
A300 105,5 m
A310 106 m
A319, A320 , A321 112,5 m
A330, A340 108,5 m
A380 104,4 m
Consequently, all Airbus models have the capability to be operated with 125m RVR at takeoff.
Additional requirements are as follows:
- Low Visibility Procedures are in force
- High intensity runway centreline lights spaced 15m or less and high intensity edge lights spaced 60m or less are in operation
- The 125m RVR value has been achieved for all of the relevant RVR reporting points
- A visual segment of 90m is available from the cockpit at the start of the takeoff run
- Flight crewmembers have satisfactorily completed a training in a simulator approved for this procedure.
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I do agree with your math.
a) 90 m must be available under mnm RVR 125. With A32S cutoff angle at 12,5 m, this is satisfied with a margin, actual segment is 112,5. This is airframe geometry requirement.
b) If you see 6 lights = 90m of pavement, how much slant range you have? 90+12,5 = 102,5 m slant. The above wording suggest that crew shall check this condition is complied with at the start of take of run.
- Can you replace low reported RVR value in the first third with a cockpit assesment for 125 m LVTO?
- Can you substitute a missing RVR reading in the first third with a cockpit assesment for 125 m LVTO?
- Do you comply with 125 RVR rule by having 102,5 SVR as observed from an Airbus cockpit (i.e. 6 lights spaced by 15 m apart?
I asked these before and got answers. Answers I could understand and agree with. The only problem is, they contravene each other.
Good luck,
FD (the un-real)