Aero-News has received a copy of a recently published safety notice issued by the Southwest Airline Pilots Association (SWAPA). In direct response to concerns raised by SWA's tragic December MDW over-run, SWAPA has clarified and issued the following report. ANN confirmed the authenticity of the document with SWAPA members, who were "not surprised" that it was being disseminated so quickly. The document is attached below without editing, though contact names and email addresses were redacted for privacy's sake -- Jim Campbell, ANN E-I-C

Subject: WINTER WEATHER OPS Safety Alert 2006-01
From the Southwest Airline Pilots Association (SWAPA)
January 23, 2006 
WINTER WEATHER OPS Safety Alert 2006-01

Although there is very little that can be discussed concerning the MDW Flt. 1248 accident of Dec. 8, 2005, there are some facts that have come to light that need to be highlighted as at least three months of winter remain.
 
There is a distinct difference in how the OPC computes landing and RTO performance for the classic fleet of Boeing 737's and the NG -700 aircraft. The classic OPC does not utilize any reverse thrust credit while calculating the stopping margin; this is in line with the certification procedure for the aircraft. The NG aircraft OPC's however use Boeing proprietary software that factors in the use of reverse thrust for these same calculations, which in our estimation does not give you, the operator, a realistic margin of safety when interpreting how much stopping margin is actually available. Obviously SWAPA is not in the position, nor do we  have the authority to dictate operational procedures for Southwest Airlines, but in our opinion it would seem wise to review the -700 OPC data and when the runway is short, contaminated, or braking action reports are less than good, that you give consideration to programming the OPC to MEL the thrust reversers and note the difference in stopping margin. This applies to both landing performance and RTO performance; make the landing or departure decision accordingly.
 
Braking action reports and runway friction reports very often do not correlate. The braking action reports are subjective and not only is the MU interpretation subjective, the MU value does not translate to any braking action value. One can find a poor braking report followed by a MU value that ranks as the lower end of GOOD, so be very careful when relying upon the combination of both. All Part 25 certificated aircraft have their landing performance derived from dry, uncontaminated runway performance data that then has various equations applied. The formula for these equations appears to have come from a 1961 Convair 880 test that was conducted by the FAA.

The point in explaining this is that when your stopping margin begins to get a little thin it would be a good time to review all of your options as the data that you are utilizing may not actually reflect the true stopping distance required. If in fact what we are discovering is true, then the equations that were developed were  developed from a first generation swept wing pure turbojet transport. The adaptation to the current NG B-737 may not be as accurate as we have thought.

Boeing has provided us a very good aircraft to operate and one that has a great record. As pilots, we often take the performance values for granted; in most conditions that is a safe and wise decision. While operating in winter weather conditions, heavy aircraft, short runways, etc., give extra consideration to your dispatch release, the fuel on board, the runway condition, possible tailwind component, and how closely your aircraft might be to its operating limit and safety margin for that particular approach or departure.
 
We operate from some relatively short runways in some cities to fly long distances and the RTO stopping margin can be a factor. ISP comes to mind where we routinely use RWY 33L which is only 5186 feet long. A -700 in excess of 130,000 pounds will not have much in the way of RTO stopping margin departing that runway. Using the same example, a 125,000-pound -700 will not have much stopping margin while landing on that runway. Consider less tanker fuel coming in and utilizing RWY 6/24 as opposed to the often advertised 15/33. ISP in particular causes us concern as it is a high use General Aviation airport and the ATIS and active runway are often tailored to that spectrum of aviation as opposed to Part 25 aircraft that could have a greater safety margin by utilizing a longer runway. Just because the 15R/33L runway is being advertised does not mean that you have to use it.

Examine the OPC for all runways and choose the stopping margin that gives you the better safety cushion. This thought process applies to MDW as well. Historically, the active runway at MDW is predicated upon ORD landing  flows. If RWY 13C is better suited for your arrival then make the request if it makes sense. MDW ATC can provide you with that runway if asked and given the reason why. Take this type of thought process and apply it to any airport that you might be operating to or from and make the decisions that you need to make accordingly. As always, the captain is the final authority on the safe operation of the aircraft.
 
Another issue that has come to light is the periodic difficulty in actuating reverse thrust in the -700 aircraft. Through testing we have found that the slightest forward movement of the Thrust Levers will mechanically keep the Thrust Reverser Levers from unlocking. It is very important that the Thrust Levers be flat against the Idle Stop before attempting to actuate the Thrust Reversers. If you experience any difficulty in actuating the Thrust Reversers, assure that the Thrust Levers are physically flat against the Idle Stop and re-attempt. If the problem persists, then make a logbook entry and have maintenance examine the system.

-SWAPA Air Safety Committee
 
 Jeff Hefner, Chair SWAPA Air Safety
 Steve Swauger SWAPA Air Safety
 John Gadzinski Go Team Operations SWAPA Air Safety

FMI: www.swapa.org