TNCM VOR Y 10 - CDFA or Non CDFA ?

I would think the required visibility from 1000 feet MDH to see the threshold and to use a 3 degree stabilized descent to the runway is going to be at least 3 SM or more like 4800 Meters.

MxLt wrote:

So, as the minimums for this approach at TNCM are published for CDFA, it seems that we should add 200m to the RVR if we fly the non CDFA ?
Do you agree with that?

Yes that should be done.

But this is theory only: If you stay above the MDA until you see the runway and have a visibility of only 1700m (.9 NM) at the time you see the runway you had to descent about 1000ft on the remaining .9NM – that equals to a descent angle of more than 10°. Good news: With a required glide ratio of 5.5:1 you would be able to do this in almost every airplane with all engines inop ;-)

(P.S.: Yes, I’m fully aware that a RVR does not mean that you can not see the runway from further away from the air esp. in situations with ground fog/haze – but the general point holds tru that with a DH of 1000ft you need to decide for final descend early to do a stabilized descent and so the difference between a step-down and a CDFA is in practice not really big…)

Mxlt – your email address is duff so you won’t get any notifications.

Actually an aircraft doing a dive and drive is poised to do a go around assuming they leveled at the MDA.

Hi NCYankee my point applies to a large transport jet, but also to puddle jumper MEP with one engine inoperative. When configured for landing and flying level these approaches are designed to assume one engine is inoperative if a go around is required. To accomplish this, there is a phase where the aircraft has to accelerate in level flight while cleaning up to establish Vy with OEI. This is one of the main reasons why CDFA is a requirement for commercial air transport, the aircraft has energy at DA to achieve a pitch up to Vy while cleaning up. On a precision approach it is not unheard of, however, that the undercarriage of a heavy might touch the runway during go around due to inertia. The very large excess thrust of a commercial jet only applies when cleaned up.

I sort of think this point is implied as this approach is only available to A and B approach speed aircraft.

Ibra wrote:

I tend to add 300ft if air is vey turbulent & instruments are sluggish with my sloppy flying

If you do that (and I agree it’s generally a good idea), the discussion becomes a bit obsolete:

MDH is about 1000ft about threshold. So adding 300ft would be 1300ft above the threshold. With a stabilized 3° final approach (which is roughly 300ft/NM), you need to start the final approach at approx. 4.3NM before the threshold.
FF10 is 4.8 NM out.

So the “CDFA” which is shown on the chart is actually exactly the flight path of the non CDFA with some safety margins added…

Also at the charted minimums there is no way one could complete the procedure using the CDFA technique as it would require more than three miles visibility to see the runway at the MDA. It is also restricted to Category A and B.

RobertL18C wrote:

A 1,555 foot hill at the end of the runway might want you to think again about dive and drive?

A swept wing transport in landing configuration is not exactly poised to go around from a dive and drive.

Actually an aircraft doing a dive and drive is poised to do a go around assuming they leveled at the MDA. They may or may not be poised to continue a descent to the runway, but it is always easier to commence a pull up from level flight verses descending flight.

AFAIK, CFDA & non-CFDA minima are the same, it’s the same MDH, for both up to you to make sure that you don’t go bellow MDH on MAP: some will suggest you add 50ft, 10% of your ROD…

To be on the safe side, I tend to add 300ft if air is vey turbulent & instruments are sluggish with my sloppy flying