Wednesday, January 7, 2009

Flying the CAT 1

It's been a few days since my last post, and my conscience (or is it my ego?) has been bugging me to get back at it. I've got a lot of personal introspective writing to do in the next week for a church discipleship group I'm in, so I thought I'd write a fun piece about something we get to occasionally do in my job. It's also serious, demanding, and pretty satisfying as a pilot.

This posting's title doesn't signify Air Force One flying a first family cat around. CAT I actually means Category I, referring to a type of instrument approach we do, an 'ILS'. ILS stands for Instrument Landing System, and on a Cat I ILS (there are Cat I, II, and III) we can fly an approach down to the runway with visibility as low 1/2 mile or 1800 feet, if the runway has the proper approach lighting. There are no legal cloud ceiling minimums for us to fly an ILS, although the standard minimums published on the approach procedure maps (plates) is a 200 foot ceiling (the altitude above ground where the clouds start).

The ILS has been around now for about 50 years or more, and it's a reliable system. Flying down through the clouds, mist, rain, and snow to breakout of the clouds with the runway right in front of you is pretty neat, but it can be pretty challenging, depending on the weather and the quality of equipment your aircraft has. The ILS is a precision approach system, the horizontal guidance corridor (localizer) is 3 degrees wide, the vertical guidance corridor (glideslope) is 1.4 degrees thick. In a jet, a hand flown, 'raw data' approach to minimums is difficult, rare, unwise, and could be dangerous if not flown precisely. Some pilots say 'real men' will hand fly an ILS down to minimums, in truth 'professional men' will use the autopilot and flight director. More about that later.

The ILS has a few components, but the two main parts are the localizer and the glide slope. Both are ground based, VHF radio (Very High Frequency) navigation signals. Both transmit at a frequency a little above the FM radio range. The localizer is transmitted from an antenna aligned with the runway, while the glideslope transmitted from an antenna right next to the runway, 1,000 feet after it's beginning (this is our intended landing point). Each runway which has an ILS has a specific frequency for it. We tune that frequency and our flight display screens will show two needles: (1) a vertical needle, the localizer, which shows the aircraft's horizontal position in relation to the extended runway centerline; and (2) The glideslope, a horizontal needle which shows the aircraft's vertical position in relation to a 3 degree approach down to the end of the runway. When the aircraft is centered on the localizer and glideslope courses, it looks like the cross hairs of a rifle scope.

In mid December, on one of my many BNA overnights, Nashville was reporting a nice 200 foot overcast cloud deck with 1/2 mile visibility and mist, and the winds were calm. Nashville approach told us to expect the ILS 2Left. The following is a link to the approach procedure: http://www.avn.faa.gov/d-tpp/0813/00282I2L.PDF It was my FO's turn to fly, and he was ready for the opportunity. At the regionals, many newer CA's tend to take the more difficult approaches, and I think he appreciated that I showed confidence in him. We got setup for the runway (oriented basically to land to the north on the most western runway) with our radios and settings. Then he briefed the approach, and the missed approach, a prescribed climbout procedure for each approach, in case we didn't see the approach lights or runway at the minimum height permitted (DA, Decision Altitude). In this approach the DA is 799 MSL (altitude above mean sea level), and 200 above the runway. Actually, we can descend down to 100 feet above the runway without seeing the runway, if we have the approach lights in sight at the DA. If we don't have the runway in sight at 100 we have to go around as well. Clear as a cloud layer?

It was pretty above the undercast, the glow of the city lighting the clouds. Many times there are layers of clouds and you don't have defined cloud tops as we had this evening. BNA approach gave us the final vector and approach clearance as 'Chris' slowed and had me configure our RJ with flaps and landing gear.

We have quite a bit of teamwork in flying an ILS. Narrative from this point is our standard call outs as follows: ATC, PF (Pilot flying, Chris), PNF (guess):

ATC: 350 heading to intercept, 4 miles to DIKINS, cleared ILS 2 Left, contact tower 118.6.
PNF: (repeat that back).

PF: Nashville tower, __ __ ILS 2 Left.
ATC: ___ ___ cleared to land runway 2 Left.

PF: localizer alive
PNF: localizer alive.

PF: Set missed approach altitude 4,000.
PNF: 4,000 set.

PF: glideslope alive
PNF: glideslope alive.

PF: Gear down, landing checklist
PNF: (repeat).

PF: Flaps 30, 160 (speed)
PNF: (repeat).

PF: Flaps 45, Vref plus 5.
PNF: Flaps 45, 142.

PNF: Landing gear?
PF: Down, 3 green.
PNF: Down, 3 green. Flaps set 45, indicating 45, landing checklist complete.

PNF: 1,000 to minimums (at 1,799 ft per the approach plate)

PNF: 500 to minimums (1,300)

PNF: 100 to minimums

PNF: minimums, approach lights in sight
PF: continuing.
(immediately thereafter) PNF: runway in sight
PF: landing

All this happened in just over two minutes. At 150 knots, 2.5 miles per a minute, it goes by fast, but also because we're busy. We train to fly ILS approaches to minimums in the simulator quite a bit, even with one engine failed. In real life I fly an ILS to minimums only half a dozen times a year it seems, so it always seems special, and it's always important to get it right. It's exciting too, the anticipation builds as we get closer to landing, as does my heartrate. Are we really going to breakout this close to the ground and land as expected, or will we 'go missed', climb out and try again or enter a holding pattern and wait for the weather to improve? It's easy to let yourself tense up when flying an ILS, especially if you're hand flying one, the trick is to be relaxed but responsive and ready to land, or go missed if needed. You see, that's why they call it a Decision Altitude.

Frequently, the transition from instrument flight to visual flight, based on what you see outside, can be tricky. Chris made a very nice landing moments later. We had no depth perception at all, but he made a nice tire chirping, nose up touch down and smooth roll out. Yea, we had broken out of the clouds and now saw the runway, but because it was illuminated by the very bright edge lights and touchdown zone lighting (two columns of lights in the runway surface showing the preferred area to land on), neither of us could actually see the runway itself. They keep the lights on brightly so you can see it through the mist and fog. This is where experience and skill came into use. The jet has a radio altimeter which calls out audibly the height above the runway, it counts down 50, 40, and so on down to 10 feet. At the 10 call I said 'pitch looks good' (a non-standard call out, but it sounded good), referring to our pitch attitude on the attitude indicator and from the view of the runway. You don't want to land this plane (or any plane) with the nose too flat. I don't think Chris needed the help though, with basically the same pitch angle, we touched down shortly afterwards.

And that was basically our recent ILS 'down to the nuts' as they say (pilot lockeroom slang). I've had a few that were really close, seeing the runway right at 100 feet. You taxi in slowly because of the fog, with your fingers and feet all tingly after those. Technology is great, but our plane is far behind state of the art. There are jets that will automatically land, brake, and use thrust reverse, all you have to do is watch (with baited breath); they require minimum 600 feet visibility I think. Others have figher jet like heads up displays (HUD's) which show an artificial picture of the runway in front of the windshield, this enables almost auto-land like minimums. Here is a link to a you tube video of a foreign 737 crew doing an auto-land CAT III approach in CAT I weather conditions, very much like what we experienced at Nashville this night: http://www.youtube.com/watch?v=nNDImUfSN8Q

About that autopilot too: if you have technology, why not use it? A better measure of a man, as far as being a pilot goes, is along these lines: How do you manage risk, make decisions, lead others, exercise good judgement, and be in command? Successfully hand flying an ILS down to minimums without an autopilot or flight director (a flight director shows the pitch and bank attitude the auto pilot would fly if it was engaged) shows a great level of skill of the pilot, but not a great level of judgement. One of the risks of hand flying a raw data approach is that the plane won't be aligned properly with the runway at the DA, consequently that would make a landing attempt unsafe, and a missed approach more likely.

On the other hand, we pilots like to think that we can still hand fly an approach, 'if we had to'. It is difficult to do so in this jet, it takes a smooth and responsive hand, and a quick and rythmic instrument scan to fly a good raw data approach, it's intensive work! Much easier to monitor the plane and autopilot, and let it do the hard work.

Our company has standards for flying approaches. They prefer that anytime the weather is less that a 1,000 ft ceiling or 3 miles visibility that we use the autopilot and flight director. I try to abide by that requirement; my personal preferences are almost that: 1,500 and 5 - raw data, 1,000 and 3 - flight director, 500 and less than 3 - autopilot.

I'll probably fly a couple more 'tight' ILS approaches before the winter is finished, and I'm bound to have a couple this spring. We can get some nice fog in CLT, and a few other places. When the weather adds a heavy rain, winter precipitation (snow, freezing drizzle etc.), and/or a crosswind to a low ceiling and visibility, then we really start having fun. Well, you know what I mean, right? Comes with the territory, as they say.

I'm blessed to be able to do what I do, to have a wife and family who support me, and to have parents and relatives who helped me get here. Till next time . . .

2 comments:

Shannon said...

I like the video - good choice! Maybe if I talk in autopilot monotone speak that would work at home? Make bed. Pick up girls. Clean bathroom. Just kidding: ) I might try it though! Love you!

Mom said...

What raw faith it takes to do what you do...so well written that I was right there with you.