January 17, 2011

At the Edge of Safety

The following was originally posted at  www.aviationschoolsonline.com/blog  Check out their site to view more recent posts by other authors. 

Do you remember the details of your last drive to work? If the weather was nice and the roads were in good condition, you probably don’t. How about the last time you topped an ice covered bridge in the winter with a stout wind blowing from one side to the other? I remember the last time that happened to me in great detail. Tightened grip on the wheel…concern and accuracy with the placement of my tires on the rough…enter the bridge slightly upwind if possible…mildly elevated heart rate. At my job as an MD80 First Officer, I rarely remember the specifics of a particular day or individual landing. I go to work, fly from here to there, layover and do it again the next day. My internal autopilot often engages and things just seem to happen on their own. Don’t get me wrong, I take every flight seriously and devote my professional existence to performing at my best, but as many times as I’ve landed this airplane, things begin to happen without consciously thinking of every move. However, every now and then I find myself in a situation that gets my heart beating and adrenaline flowing. 



Climbing out of DFW this morning on our way to Minneapolis, I pulled up a current weather report so the Captain would have the most up-to-date weather information to pass along to the passengers when he made his next PA. I was surprised to see that the conditions at the airport were worse than forecast with strong crosswinds, visibility around 2 miles and light snow. When I signed in early this morning, I checked the weather along our route and at Minneapolis, our final destination. The visibility was hovering around 3 miles in light snow with crosswinds blowing steadily at 18 knots and forecasts predicted improved conditions with diminishing winds and improved visibility as the day went on.
I really wasn’t overly concerned about the weather reports. Snow and wind is part of the deal when flying up north this time of year and today’s weather was no exception. As we continued, I kept an eye on airport conditions, retrieving new reports about every 30 minutes, checking for special reports and hourly observations. As we began our descent from 35,000 feet, I checked the weather one last time and discovered that the visibility had dropped to ¾ of a mile in snow with wind blowing directly across the runway at 24 knots.

The Captain and I both began to wonder about crosswind limits and retrieved our operating manuals to verify the limitations in diminished conditions. These numbers are the sort of thing they ask us every year in training, but since we rarely operate near the limits, it’s always a good idea to check your memory against the books. The maximum demonstrated crosswind for the MD80 is 30 knots on a runway with good visibility and favorable braking action reports. Reduce the braking action report to fair, and the crosswind limit drops to 20 knots. Reduce the visibility below ¾ and the max crosswind limit drops further to 15 knots. The current visibility at the airport was ¾, which was just enough to avoid a crosswind reduction, but with snow and ice on the runway, we were concerned about braking action reports. We would have to wait until we got a hand-off to Minneapolis approach before we would be able to get an accurate braking action report, so we continued preparations for landing.

The Captain briefed an ILS to runway 12R and I tuned and identified the frequencies. We continued our descent as I completed the Descent Checklist and got started on the Before Landing Checklist. I flipped the switch on our number one radio to check on with approach and overheard a Delta jet inquire about the winds. The wind was still blowing directly across the runway with gusts to 24 knots, but the controller relayed a braking action report of “fair.” As I mentioned before, the crosswind would have to be less than 20 knots before we could land with a fair report. I waited for a break in the radio congestion and informed the controller that we would be unable to land. “Say your intentions“ he said.  I requested holding then explained that we needed a braking report of “good” before we could accept the approach. MSP approach informed us that the “fair” report was from a much smaller aircraft and that they would get reports from larger aircraft ahead of us on the arrival.

There were several Delta A320s on the arrival in front of us that seemed content with the winds and continued the approach. I was a little surprised that their limits would be different than ours, but I was also pleased that someone ahead of us could land and hopefully report better conditions on the runway. A report of braking action “good” was reported by the next aircraft and we accepted an approach clearance. There were now two Delta jets ahead of us on the approach and as we passed 3000 feet on the glide slope, the first relayed another report of “fair” but the aircraft in front of us landed and passed along another “good” report. We were legal to land.  

The back and forth reports of the conditions on the runway concerned me greatly and present an opportunity to mention the different and sometimes contradictory terms legal and safe. There are a great many times in aviation that an action may be legal, but not safe. There are probably a number of examples of safe, but not legal, but none come to mind at the moment. Our manuals and the Federal Aviation Regulations determine the rules by which we operate our aircraft, but the legal minimums don’t always take all relevant factors into consideration and sometimes don’t provide enough of a margin for safety. For the MD80, the maximum crosswind limitation for a runway with braking action “good “ is 30 knots. The crosswind today was gusting to 24 on a snow covered runway with suspect braking reports.  Legal?  Yes.  Safe?  That’s up to the pilot. How long is the runway? What type aircraft made the report? How experienced was the pilot and do you trust his subjective opinion of the conditions? All these things come into play at this point of the process and they are all valid considerations. Legal is not always safe, and the decision isn’t always easy and is never made in a vacuum.

There are other considerations as well. The vast majority of the approaches we fly provide ample room for mistakes and malfunction, but while incredibly rare, system malfunctions do occur. An airplane is an incredibly complex machine and sometimes things go wrong within landing critical systems like brakes, anti-skid, spoilers and reversers…sometimes at the most inopportune moment. When operating into an airport near sea level with long runways on a day with favorable weather conditions, there’s automatic room for error and abnormality. Dallas, Ft. Worth International, for instance, is an airport where the runways, at only 600 ft. above sea level, are almost all longer than 13,000 feet in an area of the country that enjoys generally mild weather conditions. I realize you might take issue with that statement in August when it’s 113 degrees outside, but compare DFW to Minneapolis and the approach we flew today with an 8,000 ft. runway covered in ice and snow where the winds were blowing directly across the runway at 24 knots and what you have is an approach and landing at the maximum capability of the aircraft. On an approach like this one, very little can go wrong without dire consequences. The Captain and I determined that we were legal and decided it was safe to land, so we proceeded with the approach….carefully.

The Captain was at the controls and I assisted him as best I could with regular callouts regarding our speed, altitude and changes in the wind as we continued down the glide-slope. We completed our landing checklist and were stabilized on the approach well before the required 1000 feet. When I say stabilized, what I mean is that we were on speed, on glide-slope, engines stabilized and properly configured. Statistics show that the chances for a successful approach and landing are far greater when the aircraft is properly configured for landing and stabilized on the approach by 1000 ft.

The wind was gusty and we experienced plus and minus 10 knot fluctuations in airspeed most of the way down final, but the Captain put the aircraft right in the touch down zone, the auto brakes and auto spoilers deployed as planned and we stopped with plenty of runway to spare. As we slowed to taxi speed, the anti-skid began to release the brakes in an effort to maintain traction, but I would have to say that I agreed with the preceding jet’s assessment of the braking action and we passed along our own report to the tower.

You know that feeling you sometimes get after driving home from work when you can’t remember exactly how you got home? We didn’t feel that way after this landing. We cleared the runway and taxied to the gate with a sense of relief, and maybe a little pride, for a job well done. Hats off to the Captain for shooting the perfect approach in some pretty awful conditions. Go to work. Fly from here to there. Layover and do it again the next day. When we return in the morning, hopefully the line between safe and legal won’t be so thin.
 

6 comments:

  1. Another great read. Legal is not always safe. My stress meter goes up during Winter Ops. Runway contamination and its impact on braking effectiveness is always a consideration. Factor in the wind and the uninformed can quickly get themselves in trouble. I recently delayed a trip by 24 hours for a Winter storm in Western Montana. One of your company planes had a problem in Cody, Wyoming the same day. My principal passenger called me and asked if it would be okay the next day even after the delay, given how bad the conditions were that he was experiencing. Fortunately, everything worked out great. Thanks for sharing!

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  2. It always astounds me that one snowflake in Chicago will get ORD all tied up in knots, while it takes a full fledged blizzard with gusts and blowing snow to impact MSP. After living in the upper midwest you just get used to driving slower and being more cautious. Goes for landing aircraft too I guess.

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  3. Very interesting and timely post. I was just reading a story on the B757 overrun at Jackson. It seems it took 18 seconds for the thrust reversers to fully engage, which at 135 kts means over 4,000 ft of runway is now behind you. Any idea why? When I worked on Boeings and their engines (P&W JT8's) they were still manual, and could ot have taken that long.

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  4. DB - I hate to deflect the question, but it would be unwise for me to comment on the subject in a public forum. Honestly, I wasn't there and I wouldn't want to speculate but I suspect I share your concerns.

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  5. Thank you captain for your story...I am a first time "commentputerinner", ha. I felt like I was there as well,like the times, you pass a traffic light and after going thru, you, Can't remember what color the light was..you just shake your head and keep going...saw a show on Science channel yrs ago, that people have 2 different 'eyesights'.One that you normally see, your everyday life...and the other...subliminal...where your brain gets the info, like probably with a traffic light...you looked,but the info wasn't actually put in the memory, but proper actions were taken...Isn't that cool??!! We humans are complex as well...again Thank you for sharing your adventure..looking forward to the next one! misstwa(because I really do Miss TWA Airlines) signing off ^j^

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  6. This us a nice blog.Good read thanks for sharing with us

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