Sunday, December 18, 2011
Something happened recently that I want to share with you. We made a mistake, and learned from it. As part of our SMS (Safety Management System), when we make mistakes we try to identify the root cause, and then come up with a way to mitigate the situation so we don't make the same mistake in the future.
We fly to KTEB, Teterboro New Jersey, a lot. It's where most of the corporate jets go when they have passengers who wish to do business in downtown Manhattan. It's about a 30-40 minute drive from the airport to Wall Street, and the airport has less congestion than Newark, JFK or La Guardia.
A little while ago, the plane did a KTEB trip. It was an early-morning departure, and the weather was fine. The approach in use was the ILS (Instrument Landing System) to runway 06. On a full ILS approach, the radio signal lines you up with the runway and also tells you when to descend, and if you are high or low on your descent angle. The ILS approach is the most common instrument approach in most large airports, because most airplanes that use it can fly down to 200' above the ground without looking outside, and on some advanced ILS approaches, some sophisticated airplanes can use the radio signal to fly right down onto the runway without looking outside at all - pretty handy in places like Boston or Vancouver where it can get pretty foggy.
The only unusual variable on this trip was that the ILS for runway 06 had the glideslope radio signal out of service, so the approach only offered lateral guidance, ie it would only line you up with the runway, and you had to use alternate methods to calculate when to descend.
That's a link to the ILS approach onto runway 06, so you can follow along in glorious hi-res if you have a .pdf reader.
This next part is kinda technical, and I can`t figure out how to make it less so for non-pilots, but I`ll have a summary afterwards so bear with me.
The approach is pretty straight-forward - Air Traffic Control will give you radar vectors to intercept the inbound track, which is an angle of 060 degrees to the airport. They usually angle you so that you intercept the approach track at Vings intersection. Now there are a few ways to verify that you are at Vings intersection. One way is to put the waypoint in your GPS receiver, another way is to put the 294 degree radial off the JFK VOR and the 080 degree radial off Solberg VOR and fly over where they cross each other, but another way is to dial in the TEB VOR and when you are on the localizer and at 12.5 DME (taken from the VOR), then you are at Vings. The last way is the way we chose to identify Vings.
In our SOP`s (Standard Operating Procedures), the pilot flying (the guy in the left seat) will brief the approach and the non-flying pilot will tune and identify the radios. This was done, but as the plane approached the airport, it became obvious that the airplane wasn`t quite where it should be. The weather was good, so the pilot flying was able to see the runway about 20 miles back, and lined the airplane up with it nicely.
The thing is, the navigation radios were saying that the airplane was pretty far to the left of the runway, and this caused some confusion in the cockpit. I happened to be sitting in the back on this flight, watching the flight crew, and I was also confused for a few seconds.
Take a long hard look at the approach plate, and see if you can figure out the mistake that was made. Keep in mind that the glideslope was out of service for the ILS, so we weren`t expecting to see any glidepath information, nor did we.
//edit - to add a little information, the plane was showing off-track by only a few degrees, but our localizer indicator was showing nearly full deflection even though we were lined up with the runway. As mentioned earlier, the weather was fine so the briefing was for the visual approach backed up by the Localizer (the localizer is the ILS system without the glidepath system). The pilot flying had flown this approach probably a hundred times in the past few years, but this was the first time the non-flying pilot had been into Teterboro.//
I`ll talk about what happened next tomorrow.