ILS/LOC approach MAP confusion

[flyboy0681]

I guess my checkride is still fresh enough in my mind to know that the *LOC applied only to the VDP. 

 

But give it time..

[Marauder]

I guess my checkride is still fresh enough in my mind to know that the *LOC applied only to the VDP.

But give it time..

Like everything else, "use it or lose it". Since most localizer approaches are part of an ILS, as long as the glideslope is working, you won't get much real world usage of a VDP.

And now with my new found love of LPVs, I'm finding that I rather fly one of them than an ILS. It would be nice to keep a thread like this alive. Always good to be reminded of what we forgot!

Sent from my iPad using Tapatalk

[M016576]

Another note about VDP's- if you do a thorough airport study, then the runway length in consideration to the MDA and MAP and your particular aircraft can mean that you may still be able to fly a 3 degree glideslope from the MAP and land with 4-5000' remaining at some of the bigger airports (like LMT, where we have 10300'). It can swing the opposite direction... If your runway is 4k- better get down quick like....

[Bob - S50]

I mostly agree with previous comments with one addition.  In general I would say:

 

1.  The missed approach point is at .8 DME.  However, at minimums (400') at the MAP you would be hard pressed to be in a position to make a normal landing.

 

2.  The 1.8 DME is the VDP and if you are at minimums and don't see the runway at that point, you should be prepared to go missed.

 

3.  Timing is only there as a backup if you have no DME.  If you have DME you can ignore timing.

 

Bob

[jlunseth]

I won't ever take issue with a pilot's decision, knowing his or her own capabilities, to be conservative and act on the safe side.  However, there is practice and there is real life, and in real life, other factors besides theory are often at play.  It is very important to know when something in "the book" is a recommendation, and not a requirement, and why it is a recommendation.

 

A couple of years ago I was doing an IPC with an instructor at KIXD.  We did three approaches as I recall, at different airports around the area, and we were constantly in IMC.  There were thunderstorms in the area and they were forecast to moderate at our takeoff time but stuck around.  They were not strong storms, but we were constantly on watch on the NEXRAD to avoid the "hot" cells, and we were getting tossed around the entire time we were up.  ATC was also having difficulty and we were kicked off two holds to make space for other traffic and vectored around quite a lot.  It was a real workout and we were tired and ready to be done when we headed back to KIXD. 

 

At KIXD, we found that there was a strong prevailing wind from the south, and a cell with heavy precipitation immediately north of the landing runway which was 18.  We elected to conduct an ILS 36 with a circle to land, so we would approach from the south and not need to penetrate the heavy precipitation at the north end.

 

On the first attempt we got no glideslope signal on the primary instruments, and we had not set the secondary instrument up for the ILS.  I attempted to convert to a LOC approach, but we caught the problem too late and could not get down, so we had no choice but to go missed, a "real" missed in this instance, not practice.  We were vectored back to the approach, scrambled to get both the primary and secondary instruments set up for the ILS, and this time caught the glideslope with no problem.  We descended down to CTL altitude, which as I recall was about 480 AGL.  This turned out to be right at the cloud bases, with the concern that we could lose contact with the runway at any time.  The cell was a "wall" of rain parked immediately north of the runway approach end, so we were unable to fly further north than the end of the runway.

 

I put in quite a lot of power, not wanting to make the sharp, low level, 180 turn with anything resembling stall speed, and also knowing that there would be a significant headwind to slow us down once the turn was complete.  We made the 180 with no incident, and found ourselves over the approach end of the runway at 480' .

 

There is a general rule of thumb that third approaches after two "real" misses rarely end well.  Further, we were tired and low on fuel, we had reserves, but I did not see flying to another airport outside the core of the weather system and then conducting another approach as a good choice.  The best choice was to land. 

 

The gear was already down, I deployed the speedbrakes, put in full flaps, had the prop full forward for max drag, pulled the throttle back all the way, and slowed as far under best glide as I felt was safe.  We "helicoptered" down, and at the last minute I put in a little power to arrest the descent.  The landing was a squeaker and we still had quite a lot of runway left, the runway at KIXD as I recall is about 7,000.  As the PIC I felt satisfied that my decisions were the correct ones.

 

I tell this story to demonstrate a point.  It is possible, by following the most conservative course of action, to put oneself in a position of jeopardy.   You need to know your own capabilities and the characteristics and capabilities of the aircraft.  I would certainly not recommend what I did to a new pilot, or even for me had I not been fully up to speed at that point on how the aircraft would perform.  But it is certainly possible to bring a Mooney down to a safe landing at a glideslope exceeding 3 degrees, and the same thing goes for most light aircraft like the Warriors and Skyhawks.

 

The VDP is not optional for most large aircraft.  Company manuals and procedures typically require that the PIC go missed at the VDP to prevent an overrun.  However, there is a reason the VDP is not mandatory for all aircraft, and that is that for those of us flying small aircraft, the capability of the aircraft to make a normal and safe descent at a steeper angle, particularly on a long runway, is better than the "big iron." 

 

I reiterate, I would not recommend this to a new pilot or someone "out of practice" and not confident of his or her own, or of the aircraft's capabilities.   

 

autopilot, the MAP for the LOC is 0.8 on the KSBY ILS 32.  The VDP is 1.8 .  There is no "MAP" or "MDA" for an ILS.  There is a DA/DH, and you must go missed on an ILS upon reaching the Decision Altitude unless you have 91.175 references.  If you lose the glideslope at any point or are unable to capture it, then you are immediately on a LOC approach in which case you do have a MAP, and if no DME or GPS equivalent, you should have the timer running and use time to determine the MAP.

 

Personally, I would fly to the MAP at MDA on that approach for a couple of reasons.  One, at the VDP you are still a mile from the runway and have plenty of time to pick up .175 references.  Second, if you do go missed, notice that the VOR is in the center of the airport and the missed instructions require passing the VOR and turning more than 180 degrees and approaching the hold point from the northwest or north.  To fly the missed correctly, you are going to have to fly over the MAP anyway, so instead of climbing to 700 at the VDP, why not stay at MDA to see if .175 will help you out. 

 

Learn well, stay safe.

[Audipilot1]

And... Good luck on the check ride!Sent from my iPad using Tapatalk

Thanks... We got a PASS today! I happened to shoot that approach....ILS Though.

[Marauder]

Excellent! Welcome to the club!

[47U]

FABULOUS! Congrats on your checkride. I'd like to read about the high points of the event... if you're willing. No pressure.

[flyboy0681]

 I'd like to read about the high points of the event

 

Same here.

[PTK]

Thanks... We got a PASS today! I happened to shoot that approach....ILS Though.

Congratulations on a job well done!

[xftrplt]

And, for bonus points, what does the black D at the top of the runway diagram mean?

[flyboy0681]

And, for bonus points, what does the black D at the top of the runway diagram mean?

 

Check the A/FD for more information on runway distance information.

[triple8s]

This is really good stuff! Oh congrats !