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| Title: | Runway excursion, Incident involving aircraft SE-DNU at Ängelholm Airport, M county, Sweden, on 15 April 2004 (Recommended) |
| Micro summary: | Due to a design fault with a low expected incidence, this Boeing 737 left the runway. |
| Event Time: | 2004-04-15 at 1918 |
| File Name: | 2004-04-15-SE.pdf |
| Publishing Agency: | Swedish Accident Investigation Board (AIB) |
| Publishing Country: | Sweden |
| Report number: | RL 2005:14e |
| Pages: | 16 |
| Site of event: | Ängelholm Airport runway 14 |
| Latitude/Longitude: | 56.17°N 012.52°E |
| Departure: | Stockholm-Arlanda Airport, Marsta, Sweden |
| Destination: | Ängelholm-Helsingborg Airport , Ängelholm, Sweden |
| Airplane Type(s): | Boeing 737-600 |
| Flight Phase: | Landing |
| Registration(s): | SE-DNU |
| Operator(s): | SAS |
| Type of flight: | Revenue |
| Occupants: | 115 |
| Fatalities: | 0 |
| Serious Injuries: | 0 |
| Minor/Non-Injured: | 115 |
| Other Injuries: | 0 |
| Executive Summary: | The aircraft, a Boeing 737-600, landed at Ängelholm Airport runway 14. When the speed had decreased to approximately 60 knots and the pilot in command had taken over the steering on the runway using nose wheel control, the aircraft suddenly started a yaw to the right. With nose wheel steering, rudder and differentiated wheel-braking, the commander attempted to steer the aircraft back on course, but without success. After rolling a further 100 metres the aircraft left the runway, finally coming to a standstill with its nose wheel just outside the right runway verge. Nobody onboard was injured and the disembarking was performed without problem. No technical fault has been found. Similar faults have occurred on this aircraft type before with an failure rate lower than one per 100 000, flights (<10E-5). In the manufacturer’s judgement, course can be maintained using the rudder irrespective of the angle of the nose wheel if speed exceeds 40-50 knots. It is considered that the effect of an uncontrolled yaw at this speed is limited since the aircraft can normally be stopped with the wheel brakes before it has left the runway. The aircraft manufacturer therefore classifies this type of incident as a ”Major Event” and not “Hazardous”. As the failure rate is lower than 10E-5 the manufacturer considers it acceptable and that no measure to deal with the problem is necessary. FAR125. also states that a failure rate lower than 10E-5 is acceptable for commercial aircraft faults defined as ”Major Events The Swedish Accident Investigation Board shares the aircraft manufacturer’s classification of this malfunction and incident as a ”Major Event” rather than ”Hazardous” and the consideration that a failure rate lower than 10E-5 can be accepted. The incident was caused because the design of the nose wheel steering on this aircraft type permits a spontaneous turn without operation by the pilots. A contributory factor is that the aircraft manufacturer considers the malfunction to be acceptable if the failure rate is lower than 10E-5. |
| Learning Keywords: | Operations - Runway Excursion |
| Operations - Upset - Uncommanded or excessive Yaw | |
| Systems - Landing Gear | |
| Systems - Landing Gear - Nose wheel steering |
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