Allan
24th Mar 2005, 19:00
My company operates a mixed fleet of 737 Classic's and NG's. During a review of our procedures, attention have been drawn to the subject: How do you construct a procedure on how to fly a non-precision approach as a continuous descent approach and still have the same procedure for both the classics and NG's and also use available systems to an optimum level. For instance, we cant just go LNAV/VNAV, because on the classic's the FMC shows the old blockspeeds, e.g. flaps 5/170 kts, no good. The FCTM states the you should add 50' to your MDA and then use that altitude as a DA, do you do that?? When do you reset the altitude selector to missed approah altitude? Anyone any thoughts???
Kind regards
Capt Veeclean
24th Mar 2005, 19:32
Hi Allan,
How indeed!
With autopilot and autothrottle engaged -
By flying a 3 degree / 5.2% slope towards the threshold, ensuring that you do not go below any minimum altitudes. Use the DME distance vs. altitude table on the approach plate - use the groundspeed vs. ROD table as well, or use the 5 X groundspeed = ROD rule to maintain the nominal glideslope.
If there is no DME, put the R/W -/.1 miles (an along track fix) in the fix page, to indicate approximate distance to threshold. In the NG, the FMC accepts the R/W as a fix (well, update 10.5 does, anyway!).
Adding 50' to MDA is indeed in accordance with JAR-OPS rules for CAT C aircraft - round this up to the nearest 100' in the MCP altitude window.
Standard Boeing procedures advise resetting missed approach altitude at 300' above MDA. This is because Boeing procedures assume automatic flight and this avoids the A/C levelling off at MDA, which may not enable the A/C to continue on a 3 degree slope and therefore be unable to complete a stable approach to landing. If suitable visual reference is not attained at MDA, go around - it's not possible in a jet to maintain MDA , then dive towards the runway when eventually visual!
Remember to reset the F/Ds after MDA is set, to enable TO/GA mode after a go-around.
Hope this helps.