Visual Descent Point Hazards

Visual Descent Points are a relatively new phenomenon in the instrument flying world. Much like GPS approaches and integrated glass panels, they were a rarity when I was working on my instrument rating in the mid-late 90’s. But time marches on, and the dreaded NDB procedures and vacuum systems have been replaced with what is best summarized as “newer technology”.

However, unless you’re flying a Category III-B approach, at some point prior to landing the pilot must still make the transition to flying visually. That’s where the Visual Descent Point (VDP) comes in. It’s described this way in the Pilot/Controller Glossary:

VISUAL DESCENT POINT- A defined point on the final approach course of a non-precision straight‐in approach procedure from which normal descent from the MDA to the runway touchdown point may be commenced, provided the approach threshold of that runway, or approach lights, or other markings identifiable with the approach end of that runway are clearly visible to the pilot.

The problem with a VDP is that once a pilot meets the following requirements for descending below MDA, they are assumed to be also be flying with sufficient visual reference to avoid any obstacles that may stand in their way even though that is not one of the regulatory requirements for using a VDP.

It stands to reason that if you can see a runway three miles away, you should also be able to see a tree half a mile away. Unless you’re flying at night, of course. In that case, you could end up like the pilot of this Lear 45 whose wing cut eight feet off the top of a tree while properly flying a VDP into Sarasota Springs, NY.

The weather at Saratoga Springs, N.Y. on the night of July 13, 2008 was 1,100 overcast, one-and-a-half miles visibility with moderate rain, and wind calm. Albany approach control vectored us for a GPS approach to Runway 5. We intercepted the inbound course toward the airport. On our descent, all altitudes and altimeters coincided with the information on the approach plate. Before reaching minimums, my co-captain called, “Runway in sight, twelve o’clock.” I responded, “Going visual.” Looking up, I saw the runway was dead on at 12 o’clock. Before going visual, all indications on the flight director were centered and exactly where I wanted them. My co-captain called, “Ref plus thirteen,” then immediately called, “Trees! Pull up, pull up.” I simultaneously went to max power and rotated to a 15-degree deck angle. The aircraft hit a pine tree and, we learned later, cut eight feet off its top. I still had the runway in sight, and after making a quick scan of the panel I replied, “We have good gear indication, and pressure is up; I plan on landing.” My co-captain replied, “I concur.”

Visual inspection after landing revealed substantial damage to the left wing of the Learjet 45. We learned later we had made the right decision to land from the approach and not attempt a go-around. The left flap was damaged severely enough that flap retraction on the go-around would likely have resulted in a split-flap condition that could have been catastrophic so close to the ground.

You might be thinking that he must have made a mistake somewhere, but it turns out that the procedure was flown exactly as charted. Read the full article. Since the whole raison d’etre for having instrument procedures is to avoid hitting things, this is worrisome.

Visual descent point on the GPS approach into Sarasota Springs

Most VDPs utilize a standard three-degree descent angle to the runway. According to TERPS criteria, a 34:1 obstacle clearance plane should be kept clear to ensure aircraft can fly the charted VDP path safely. In this guy’s case, he was flying — at night — into an airport which had numerous trees sticking up into that three degree path.

His story raises several questions. Are the VDP portions of instrument approach procedures flight checked by the FAA, and if so, how often? Does anyone monitor the area around an airport for tree growth or the unannounced addition of man-made structures? If so, how often? How often are charted obstacles re-surveyed? And most importantly, what accommodations should pilots make to charted Visual Descent Points at night for dark, unlit areas likely to contain things that grow larger on their own?

Unfortunately, I don’t know the answers to any of those questions. But it has me thinking about the large turbojet aircraft I’m flying these days. The G-IV demands a well-stabilized approach if you want to stop before the runway does. And as a charter pilot, I’m often headed into some very random airports at the behest of clients.

Consider that substantial groupings of large trees are often found in rural areas — the same kind of areas that also have rural airports with shorter runways and little, if any, lighting of the surrounding area at night. See where I’m going with this? In a smaller aircraft with a slower approach speed, no problem. But for a Gulfstream, I can see ending up in the same situation as the highly experienced pilot in that Learjet.

And that’s just domestic flying. Think about international destinations where our TERPS criteria are not always complied with. I can’t even begin to quote the differences between U.S. and ICAO approach procedure design standards.

The Lear pilot had it right when he said it was a false impression to believe that as long as you “fly the plate” you are guaranteed protection from things that go bump in the night. Next time you’re flying an approach after dark, keep that in mind. Buyer beware, my friends.

  5 comments for “Visual Descent Point Hazards

  1. Mike
    September 17, 2012 at 10:51 pm

    Yep. I heard about this one over on the “Blood” board (AOPA forums). A HUGE eye opener for me, that’s for certain. In my ‘ignorance’ I always figured if I did my job flying the plate accurately I was safe. Silly me.

    There was quite a discussion on this ‘incident.’ It amazed me that some posters were willing to blame everyone but the FAA…it was the airport’s fault, the city council, the neighbor whose property the trees were on, ATC… SHEESH! you’d think the FAA could be RESPONSIBLE for something! Ah, there I go being silly again.

  2. December 30, 2013 at 10:37 am

    Also of note, this incident was not recorded in the ASRS, or NTSB databases, but can be found in the ASIAS database under report number 20080713857499I. It mentions the trees were only 50 feet tall, but does not give altitude or elevation data. The ainonline article is much more comprehensive.

    It sounds like a see-and-avoid / see-something-say-something situation. The odds of hitting an obstacle on a properly-flown procedure should be close to zero, but it could happen. I’ve submitted reports about charting errors to the FAA in my young career. One was corrected on the chart, one was perhaps trivial or lost in the bureaucracy, and one is now pending for the January 9 cycle. None involved obstacles on an approach path.

    p.s. The link to ainonline needs to be adjusted 🙂

    • December 30, 2013 at 10:49 am

      Hi Robert — first off, thanks for pointing out the dead link! It should be fixed now.

      I love it when people take the time to contact the charting office about mistakes they find on approach plates and whatnot. Sometimes the Feds are pretty receptive, other times it seems like moving a mountain to get a correction made. I recall an aerobatic practice area which, while it was noted on the terminal chart, had the wrong frequency posted. After literally years of trying to get them to fix it, we finally gave in and just started using in incorrect frequency.

      Speaking of errors, they are more common in the NTSB database than in the charting world. Of course, nobody relies on the accident database to navigate safely through the air, so I suppose that’s apropos.

      Thanks for reading!

  3. January 31, 2014 at 4:01 am

    I thought of more lessons to be learned here.

    An error in the ainonline article: “The VDP feature of this type of approach assures the pilot that a 34:1 slope from the VDP to the runway threshold is free of obstructions.” That might have changed at some point (?) but is currently false. TERPS provides 20:1 slope clearance from the VDP.

    Pilots must also remember that the area below MDA is never clear of obstacles. Without a VDP, the ability to land safely is only based upon visual contact with the runway environment, including any VGSI. TERPS provides 250 feet obstacle clearance at the FAF for RNAV procedures, which means if the specific chart says 3.0 degree glidepath then there is a 34:1 clearance surface sloping forward from 250 feet below the FAF minimum altitude. But it says nothing about the area below MDA. That’s why the FAA charts have a separate symbol for “visual segment below MDA/DA is clear of obstacles on 34:1 slope.” Even when that symbol is present, LNAV guidance without VDP or VGSI offers no information about where the clearance slope is located.

  4. Hosni
    January 17, 2016 at 6:05 pm

    Why some airports have VDB and others don’t?

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