Narrative:

Wind was 200/20 gust 29; altimeter 29.28 with ILS 9 reported. We wondered why runway 9 was in use. I expected we would eventually land on 27; but briefed the ILS to 9 with 40 flaps. New ATIS winds changed: slight headwind now; strong right crosswind; and gusting. We made airspeed bug corrections. I intercepted the localizer and glideslope and flew the approach coupled. We were cleared to land and broke out 1200 to 1300 ft AGL with a large crab angle. I asked the first officer for the FMC wind page: it read 40 knots crosswind. I asked the first officer to get a tower wind check. They replied winds 160 at 20 knots. We reset target speed to +10 and I continued the approach. At about 750 ft AGL I looked at the FMC crosswind readout one more time and disconnected the autopilot. FMC read 30 knots crosswind; and with the tower reporting 160 at 20; I was satisfied that we would land within the crosswind limits and continued the approach. Airspeed was bouncing around. First officer made one 'airspeed' and one 'glideslope' callout for both. I made corrections and think I responded with; 'correcting.' all IMC callouts were made. Since the field condition report was wet-good; I landed with crossed controls; left rudder and right aileron. We landed straight; on centerline; I believe on speed; and about 1200 to 1500 feet beyond the landing threshold. Speedbrakes deployed; I deployed thrust reversers to detent 2; and we decelerated on centerline; as per a normal landing; all while holding left rudder and right aileron. First officer said he had the aileron; I asked for and received confirmation that he did; and then relinquished control of the aileron to the first officer. He continued to hold right aileron and I steered straight down the centerline with rudder pedals as we decelerated. At about 80 knots; still on centerline; the first officer called 'autobrake disarm.' then at approximately 70 - 80 KTS; the nose began to move or slide to the right as the aircraft seemed to rotate about a vertical axis. I immediately applied full left rudder; but the nose continued moving right. I then brought the reversers to idle reverse; to no avail. We were now moving toward the right (south) runway edge with no steering authority at all. We departed the right (south) side of rwy 9 at about 50 knots; heading about 30-40 deg right of runway heading (120 to 130 deg magnetic). I regained steering authority somewhere during the excursion and attempted to steer between the lights and signs while bringing the aircraft to a stop on the parallel taxiway. During the excursion; the aircraft remained on hard surface. Tower advised us to call ground. We told tower that the company aircraft on final should probably go around. They did. We stopped; assessed our condition and that of the airport; but saw no apparent damage. I thought we had missed all lights and signs during the excursion; and I did not feel any impacts or collisions with any signs or lights. I reported braking action fair to the tower. The first officer got clearance and we taxied to the gate. We completed all normal checklists. Passengers all seemed fine. No one had been injured; neither passengers nor crew. I did not make any announcement to the passengers; as many of them were already exiting and thanking us. The flight attendants also thanked us; but at that time seemed unaware that we had 'gone off the runway.' the first officer sent a field condition report; I called dispatch; and the first officer did a complete and thorough exterior inspection. He found damage to the no. 1 engine; but no other apparent damage. We began the processes of securing the aircraft; reporting the incident; and all other associated activities. As I play this over and over; I cannot think of any errors that we made that could have caused the event. The threat I see is both very real but extremely difficult to quantify. That is the combination of a strong and perhaps gusty (although last reported winds did not include a gust) crosswind and a wet runway that undoubtedly does not possess a constant coefficient of friction across its entire surface. The last reported wind from tower and the crosswind readout from the FMC were both well within wet landing crosswind limitations. Yet; during rollout; after significant deceleration while tracking straight down the centerline; the nose moved right and the aircraft veered right without any pilot input to do so.conjecture could include the following: 1. Perhaps we began to hydroplane; although my opinion at this point is that we did not; at least with the main gear. Immediately following the incident I had thought that maybe we had hydroplaned. 2. Perhaps we encountered a gust on the runway that exceeded the aircraft limitations and capability. 3. Perhaps the wind at that point on the runway was stronger (and out of limits) than reported by tower. 4. Perhaps a combination of more wind and less runway friction occurred at that unfortunate instant and location. 5. Perhaps with the decreasing airspeed and large crosswind; I ran out of rudder authority just as the nose gear encountered less runway friction and/or the nose gear had been hydroplaning and/or the crosswind increased or gusted to beyond aircraft capability. 6. Perhaps I ran out of rudder authority and there was just insufficient frictional steering force between the nose wheel and runway without a hypothesized decrease in runway friction or any nose gear hydroplaning. Possibly some unique combination of these threats convened upon us at that instant. We should evaluate our wet crosswind landing limitations to determine if a little more added safety margin would be prudent. Very definitely; a few words on vmcg and directional control on the ground in the B737 would be in order during recurrent training; pts; and/or pcs. In the future; a proactive approach to include weather personnel might be helpful. I personally think that virtually every one of our captains would have continued the approach through landing given the conditions we experienced prior to the incident. At no time during the approach prior to the unsolicited nose movement did I think I would approach the limit of my own capability or that of the aircraft. I do believe; however; that when the nose started its unsolicited movement; that the wind; water; airspeed; C.G.; and runway surface challenged the aircraft to violate the laws of physics. That would not happen for me on that day; nor do I believe it would happen for anyone on any other day given the same conditions. Suspension of flight operations is always an option; albeit costly; and I commend the company for taking that approach after the incident. The go-around is also (almost) always an option. Education and simulator training and simulator practice in directional control; hydroplaning; and various types of skids are all ideas and may be valuable; but would require much development and work to standardize and bring on line. Several similar lower speed loss of directional control incidents on the ground have occurred in the industry. The very least that is acceptable is to understand this event as best we can and take some action to prevent or deter its recurrence.

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Original NASA ASRS Text

Title: B737 flight crew reports a runway excursion after landing on a wet runway with a strong right crosswind. Aircraft departs the runway at about 80 KTS and ends up on the parallel taxiway with minimal damage and no injuries.

Narrative: Wind was 200/20 Gust 29; altimeter 29.28 with ILS 9 reported. We wondered why Runway 9 was in use. I expected we would eventually land on 27; but briefed the ILS to 9 with 40 flaps. New ATIS winds changed: slight headwind now; strong right crosswind; and gusting. We made airspeed bug corrections. I intercepted the localizer and glideslope and flew the approach coupled. We were cleared to land and broke out 1200 to 1300 ft AGL with a large crab angle. I asked the First Officer for the FMC wind page: it read 40 knots crosswind. I asked the First Officer to get a Tower wind check. They replied winds 160 at 20 knots. We reset target speed to +10 and I continued the approach. At about 750 ft AGL I looked at the FMC crosswind readout one more time and disconnected the autopilot. FMC read 30 knots crosswind; and with the Tower reporting 160 at 20; I was satisfied that we would land within the crosswind limits and continued the approach. Airspeed was bouncing around. First Officer made one 'airspeed' and one 'glideslope' callout for both. I made corrections and think I responded with; 'correcting.' All IMC callouts were made. Since the Field Condition Report was wet-good; I landed with crossed controls; left rudder and right aileron. We landed straight; on centerline; I believe on speed; and about 1200 to 1500 feet beyond the landing threshold. Speedbrakes deployed; I deployed thrust reversers to detent 2; and we decelerated on centerline; as per a normal landing; all while holding left rudder and right aileron. First Officer said he had the aileron; I asked for and received confirmation that he did; and then relinquished control of the aileron to the First Officer. He continued to hold right aileron and I steered straight down the centerline with rudder pedals as we decelerated. At about 80 knots; still on centerline; the First Officer called 'autobrake disarm.' Then at approximately 70 - 80 KTS; the nose began to move or slide to the right as the aircraft seemed to rotate about a vertical axis. I immediately applied full left rudder; but the nose continued moving right. I then brought the reversers to idle reverse; to no avail. We were now moving toward the right (south) runway edge with no steering authority at all. We departed the right (south) side of Rwy 9 at about 50 knots; heading about 30-40 deg right of runway heading (120 to 130 deg magnetic). I regained steering authority somewhere during the excursion and attempted to steer between the lights and signs while bringing the aircraft to a stop on the parallel taxiway. During the excursion; the aircraft remained on hard surface. Tower advised us to call Ground. We told Tower that the Company aircraft on final should probably go around. They did. We stopped; assessed our condition and that of the airport; but saw no apparent damage. I thought we had missed all lights and signs during the excursion; and I did not feel any impacts or collisions with any signs or lights. I reported braking action fair to the Tower. The First Officer got clearance and we taxied to the gate. We completed all normal checklists. Passengers all seemed fine. No one had been injured; neither Passengers nor Crew. I did not make any announcement to the Passengers; as many of them were already exiting and thanking us. The Flight Attendants also thanked us; but at that time seemed unaware that we had 'gone off the runway.' The First Officer sent a Field Condition Report; I called Dispatch; and the First Officer did a complete and thorough exterior inspection. He found damage to the No. 1 engine; but no other apparent damage. We began the processes of securing the aircraft; reporting the incident; and all other associated activities. As I play this over and over; I cannot think of any errors that we made that could have caused the event. The threat I see is both very real but extremely difficult to quantify. That is the combination of a strong and perhaps gusty (although last reported winds did not include a gust) crosswind and a wet runway that undoubtedly does not possess a constant coefficient of friction across its entire surface. The last reported wind from Tower and the crosswind readout from the FMC were both well within wet landing crosswind limitations. Yet; during rollout; after significant deceleration while tracking straight down the centerline; the nose moved right and the aircraft veered right without any pilot input to do so.Conjecture could include the following: 1. Perhaps we began to hydroplane; although my opinion at this point is that we did not; at least with the main gear. Immediately following the incident I had thought that maybe we had hydroplaned. 2. Perhaps we encountered a gust on the runway that exceeded the aircraft limitations and capability. 3. Perhaps the wind at that point on the runway was stronger (and out of limits) than reported by Tower. 4. Perhaps a combination of more wind and less runway friction occurred at that unfortunate instant and location. 5. Perhaps with the decreasing airspeed and large crosswind; I ran out of rudder authority just as the nose gear encountered less runway friction and/or the nose gear had been hydroplaning and/or the crosswind increased or gusted to beyond aircraft capability. 6. Perhaps I ran out of rudder authority and there was just insufficient frictional steering force between the nose wheel and runway without a hypothesized decrease in runway friction or any nose gear hydroplaning. Possibly some unique combination of these threats convened upon us at that instant. We should evaluate our wet crosswind landing limitations to determine if a little more added safety margin would be prudent. Very definitely; a few words on Vmcg and directional control on the ground in the B737 would be in order during Recurrent Training; PTs; and/or PCs. In the future; a proactive approach to include weather personnel might be helpful. I personally think that virtually every one of our Captains would have continued the approach through landing given the conditions we experienced prior to the incident. At no time during the approach prior to the unsolicited nose movement did I think I would approach the limit of my own capability or that of the aircraft. I do believe; however; that when the nose started its unsolicited movement; that the wind; water; airspeed; C.G.; and runway surface challenged the aircraft to violate the laws of physics. That would not happen for me on that day; nor do I believe it would happen for anyone on any other day given the same conditions. Suspension of Flight Operations is always an option; albeit costly; and I commend the Company for taking that approach after the incident. The go-around is also (almost) always an option. Education and simulator training and simulator practice in directional control; hydroplaning; and various types of skids are all ideas and may be valuable; but would require much development and work to standardize and bring on line. Several similar lower speed loss of directional control incidents on the ground have occurred in the industry. The very least that is acceptable is to understand this event as best we can and take some action to prevent or deter its recurrence.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.