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 straightâ€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, â€œRunway in sight, twelve oâ€™clock.â€ I responded, â€œGoing visual.â€ Looking up, I saw the runway was dead on at 12 oâ€™clock. Before going visual, all indications on the flight director were centered and exactly where I wanted them. My co-captain called, â€œRef plus thirteen,â€ then immediately called, â€œTrees! Pull up, pull up.â€ 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, â€œWe have good gear indication, and pressure is up; I plan on landing.â€ My co-captain replied, â€œI concur.â€
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.
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.