In contemplating my recollection of today’s events, I can’t help but recall distant memories of Delta 191, the Lockheed L10-11 that crashed at Dallas, Ft. Worth International Airport (KDFW) in August 1985 after encountering wind shear on final approach to what was then runway 17L. I was in high school at the time and on a summer camping trip in the Colorado Mountains with a group of church friends when news of the tragedy reached me. My Dad was an L10-11 First Officer and unfortunately for me, the news I received did not include any information about my Dad. We spent another two days hiking through the mountains that week before I was able to confirm that my Dad was not involved. As it turns out, Dad was safe at home that day, but his friend and colleague Captain Ed Connors was in command of Flight 191.
There are a number of videos and audio clips available on YouTube and other sites that accurately depict the sequence of events that day at DFW, but what is rarely discussed is how little we really knew about wind shear at the time and more importantly, how poor the detecting and reporting was of such events. Today, most major airports are equipped with LLWAS (Low-Level Wind Shear Alerting System), a system comprised of 6 to 33 anemometers placed on and around an airport sensing wind speed and direction within 2 1/2 miles of the airport and our airliners have both reactive and predictive wind shear equipment to warn pilots of possible threats via aural and visual means. I feel certain, if Captain Connors had the information and warning systems then that we have today, Delta 191 would have been another flight that everyone forgot.
Today’s events come at the tail end of an otherwise uneventful three day trip. Uneventful is almost always a good thing when you’re talking about airplanes. Our day started with an early morning flight back home followed by a quick trip to Colorado Springs and back before we could call it a day. As we prepared for our flight to Colorado Springs, the Captain commented that the winds, currently blowing from 270 at about 30 knots, gusting to over 40 were too strong for us to land. The runways in use at Colorado Springs are oriented north/south, so a wind from 270 would be a direct crosswind. The MD80 we were flying boasts a max demonstrated crosswind limitation of 30 knots on a dry runway with good visibility (if you‘ve been following along, this may sound familiar). The runway was dry and there were no visibility issues complicating our arrival, but with winds gusting to 40 knots, we were going to need a backup plan. We noted that the forecast called for diminishing winds that should be below our limitations by scheduled arrival time and took off for the Springs with Denver International as an alternate.
Let me add a few words about wind shear…The best course of action is almost always avoidance. But the truth is, airlines operate into cities every day that are prone to low level wind shear. If they cancelled every flight to Colorado Springs and Denver that intersected with a wind shear report, then air travel to those cities would be practically non-existent. With these cities in particular, it seems to be the combination of their location up against the eastern edge of the Rockies and the common nature of strong westerly winds that produce turbulence and wind shear events. Pilots are taught to avoid areas of severe wind shear at all costs, but intermittent or lesser events can be navigated with good piloting techniques and extra caution.
Back to my flight…
As we approached the airport from the south, I made every effort to be prepared early for the approach and landing. Arriving from the south into Colorado Springs when the airport is landing north can be a handful even on a normal day. Approach control usually instructs us to cross the FSHER intersection at 14,000 feet on the arrival. FSHER is roughly 25 miles south of the airport, so with a touchdown zone elevation of 6,118 feet above sea level, we only have 25 miles to lose just under 8,000 feet. This isn’t a problem and can be handled without too much effort if you have already slowed the aircraft by the time you reach FSHER. The gotcha here is that a typical descent speed for the MD80 would be around 300 knots, plus or minus depending on a number of factors, and the pilots are not required to slow to 250 knots until descending below 10,000 feet. So if the pilot crosses FSHER at 14,000 feet indicating 300 knots, then getting down is going to be next to impossible since slowing from 300 to 250 will add about an extra 5 miles to the distance needed to descend.
Maybe that’s too much information, but I want to emphasize that this arrival can be a challenge even without the threat of wind shear. I crossed the FSHER intersection at 14,000 as instructed with the airspeed steady at 250 knots in preparation for our descent for runway 35R. We were then cleared to continue our descent and were given a heading to intercept the final approach course for the runway. There weren’t any aircraft ahead of us on the approach to relay reports on the airborne conditions, but Tower and Approach Control were reporting gains and losses near 20 knots on the ground surrounding the field. We elected to continue our approach and make a final assessment of the conditions at 1,000 feet on final. We wouldn't ge that far.
I slowed the aircraft and configured for landing a little early to ensure a stabilized approach and was on final approach speed, glide slope and fully configured for lading at 1,500 feet above touchdown when we got a yellow wind shear light on the glare shield. The yellow light is an indication of an “increasing performance” wind shear and is yellow to emphasize caution. Increasing performance means that we went from a tailwind to a headwind or a headwind to a stronger headwind in a short distance. Neither of these is particularly dangerous, but is a possible indication that we were entering the leading edge of a microburst. A go-around is not required for this indication, but great caution is advised and we were prepared for a possible missed approach and escape maneuver.
It is difficult for me to believe, but with 24 years of flying experience under my belt, this was my first actual encounter with “decreasing performance” wind shear outside of the simulator. This is something I train for every single time I enter the sim, but I had never actually seen one in real life, and this one was pretty mild. With the nose pointing to the sky and two JT8D-219 engines producing nearly 40,000 pounds of thrust, the jet would not climb. We were well over a thousand feet above the ground with power to spare in case the event became more severe, but it was an incredibly long 3-5 seconds before we began to exit the wind shear and started to climb away from terra firma. Once we began to climb, I asked the Captain to raise the gear, reduced thrust on the engines and cleaned up as we would on a normal flight.
We departed the area to the east where the ride was a little less turbulent and entered a holding pattern to give the conditions a little time to improve. We also wanted a few other airplanes go in and land without incident before we elected to try again. On the second approach, we added in the same safety margins as before, but encountered a relatively smooth ride down final and landed uneventfully. As we taxied to the gate, I recalled images of Delta 191. I couldn’t help but wonder if Captain Ed Connors would have made a different decision about his approach and landing that day had he been graced with the knowledge and equipment that we had on this approach. Maybe he would have executed a missed approach earlier. Maybe he wouldn’t have started the approach at all. I guess we’ll never know for sure, but I am confident the outcome would have been much different.
February 1, 2011
|Sitting in line for takeoff in Atlanta this morning|
We landed in Atlanta last night after dark with ceilings reported at 200 feet and visibility expressed in feet, not miles. The approach to Atlanta was an interesting one, the ILS/PRM (Simultaneous Close Parallel) approach to runway 10. The procedure is a standard ILS approach with localizer and glideslope indications except that it is too close to a parallel runway (9R in this case) to be flown using normal procedures. The pilot’s must be specially trained to fly such an approach and there is a page long explanation that must be read and reviewed before executing the approach. The procedures call for the pilots to monitor a second tower frequency during the approach to guard against blocked transmissions and the pilots must be alert and ready to immediately follow break out instructions from the tower controller in case another aircraft “blunders” into your airspace. You might find some humor in the word blunder, I know I did, but that is the actual word used in the FAA explanation for this approach. Here’s the actual wording…
“pilots, when directed by ATC to break off an approach, must assume that an aircraft is blundering toward their course and a breakout must be initiated immediately”
I do think it’s important to have a good laugh every now and then and I laughed out loud when I read that line approaching Atlanta last night.
|Ice forming on a heated window|
By 9am, DFW had one of it’s seven runways open and that runway was only being used for arrivals. It was another two hours before a second runway was open for use by departing aircraft. The airlines, which had preemptively cancelled hundreds of flights continued to cancel even more as the day went on. In contrast, Dallas Love Field, just miles away was unable to open all day forcing Southwest, Delta and Continental Airlines to cancel every flight out of the airport all day.
Back at the gate in Atlanta and ready to depart, our flight was held on the ground while we waited for word on the condition of the runway. At the time the gate agent finished boarding, the runways at DFW were still closed, but were expected to be open by the time we landed. An hour after our scheduled departure time, we elected to takeoff in hopes that the runways would in fact be open when we arrived. Of course, we had an alternate airport planned in case the runways were still closed when we arrived, but we certainly hoped we wouldn’t need it.
We departed Atlanta where the visibility was still hovering around CATII minimums and headed toward DFW. Just as we leveled off at FL340, we received word that one runway was open at DFW and we would be able to land. The runway was covered in ice and snow, but a short time later we were informed that several company jets had landed and reported braking action good.
Our flight plans have a column indicating forecast ride conditions. The ride forecast comes from a combination of actual reports from other aircraft and the professional opinion of a meteorologist. The forecast is expressed as a number between 0 and 5...0 being a perfectly smooth ride and 5 being something like the inside of an F5 tornado. Our ride prediction for today’s flight was a 3...not good. The ride in was terrible with moderate chop and turbulence for most of the flight. We tried various altitudes, high and low, to find a smooth ride, but it just didn’t happen. The flight attendants stayed in their seats and I kept the cabin as cool as possible without freezing people out in an effort to prevent a chain reaction of air sickness.
The landing at DFW was actually a little anti-climactic. By the time we arrived, the precipitation had ended and the airport had successfully opened two runways. We landed on runway 31R while 31L was being utilized for takeoff operations only. The runway was completely covered in ice and snow, but the braking action reports were all good and although the wind, still peaking at 40+ knots was strong, it also meant that when we touched down, we were just that much closer to taxi speed which of course just shortens our landing distance.
The biggest problem I had was getting home. My car was literally frozen to the pavement in the employee lot and the drive home that usually takes 20 minutes on a good day and 25 minutes in the heat of rush hour traffic took an hour and a half. The rest of my trip was canceled and scheduling put me on reserve beginning at 3am in the morning. I really hope they don’t call…not sure if I could get to the airport anyway. We’ll see.
Posted by APC at 9:12 PM