2014 Rans S-7 Courier accident at Cambaie (974-GL)

Accident overview and flight sequence On 12 August 2014, at about 08:30 local time, a Rans S-7 Courier identified 974-GL was involved in an accident at Cambaie (974), Réunion. The aircraft was operating a local paid general-aviation flight, described as a paid sightseeing flight, with a pilot and one passenger on board. The ULM was heavily damaged. The pilot departed from the Cambaie ULM platform at 08:00 for a tourist flight over the island. He reported that the flight proceeded normally except for very turbulent conditions over the Cimendef. After passing over the Maïdo at about 8,000 ft, he began the descent to return to Cambaie, flying over the lagoon. Near Trois-Bassins (974), the right rudder pedal suddenly sank and the aircraft entered asymmetric flight. The pilot determined that the right rudder cable had broken, but the end attached to the rudder was within the passenger’s reach. He asked the passenger to pass it to him. By pulling on the cable, he restored symmetric flight. Because the control position was very uncomfortable, he asked the passenger to take the cable back and pull on it according to his instructions. They returned to Cambaie and completed the approach without further problems. During landing, shortly after touchdown, the cable slipped from the passenger’s hands. The aircraft left the runway to the left at about 60 km/h, and the left wing struck a tree. ## Aircraft examination and cable failure The Rans S-7 is a tandem two-seat aircraft, with the pilot in the front seat and the passenger in the rear. Two cables connect the rear rudder pedals to the rudder through two guide pulleys. These cables pass over the floor between the passenger’s legs. A rigid tube connects the front and rear rudder pedals. The cable connected to the right rudder pedal was found broken at a pulley. The direction-control cable was made of stainless steel and consisted of seven strands of seven wires, for a total of 49 wires. The broken end was examined using a scanning electron microscope. Of 18 wires examined, 12 showed characteristics of progressive fatigue failure, including arrest lines and striations, representing 67%. The cable therefore failed through a progressive fatigue cracking process. The pulley showed markings at the bottom of the groove and on one of the two side walls of the groove, more than on the other. These characteristics could respectively indicate excessive tension and cable misalignment. No other damage was observed. ## Maintenance history and regulatory context The ULM had accumulated 6,313 flight hours since entering service in 2006. The last maintenance had been performed on 1 August 2014 at 6,297 flight hours. It did not include an item specifically addressing the condition of the rudder control cables. The owner stated that there had already been three breaks of this cable on the aircraft, always at the same location, since 2006. The S-7 manufacturer is based in the United States and supplies the S-7 in kit form. In the United States, the S-7 is considered “experimental,” closer to French CNSK aircraft than to ULMs. The manufacturer stated that it was not aware of similar events. It recommended an annual inspection of the airframe and moving parts in accordance with the procedures detailed in FAA Information Circular AC 43.13-1B. Chapter 7-149 of that circular addresses cable inspection. It states that at each annual inspection or every 100 flight hours, control cables must be checked. Any cable with a broken wire in a critical fatigue area, such as pulley passages or cable guides, must be replaced. The circular also describes an inspection method involving passing a cloth over the area to be inspected so that it catches on broken wires. The text emphasizes the importance of visual examination, which should allow detection of broken wires inside the cable when the cloth check is insufficient. A magnifying-glass examination and/or bending of the cable may be necessary to visually detect the presence of broken wires when suspected. The owner stated that a manual and maintenance program had been provided by the Rans importer in France. That manual contained no information on recommended cable tension, no guidance on cable monitoring, and made no reference to AC 43.13-1B. The Belgian importer, which had taken over the French market, stated that it could not sell S-7s in France, but that it recommended cable inspection every 550 hours for the S-6, a model equivalent to the S-7 but in a side-by-side two-seat version. That interval had been chosen by the importer after observing wire wear on an S-6 at 650 hours. The French decree of 23 September 1998 concerning motorized ultralight aircraft states that, to obtain an identification card for a ULM, the applicant must certify that he or she has a maintenance manual. The instruction of 21 February 2012 gives a brief description of the elements that must be covered in that manual but sets no requirement regarding detailed content or the origin of the maintenance manual. Since the event, the owner slightly reduced the cable tension and chose to install a bypass on the cable to maintain control in the event of a break at the guide pulley. In addition, he monitors the condition of the various cables and pulleys. About 950 hours had been flown without any abnormal damage being observed. For comparison, the maintenance manual for the certified Cap 10C aircraft specifies that the condition of the rudder cables must be checked at the friction plates and pulley passages. The tension of these cables must be checked to be equal to 18 ± 4 daN. These checks must be performed at least at each annual inspection and each major inspection. ## Pilot information The pilot held a ULM multi-axis license. At the time of the event, he had approximately 15,000 flight hours on the Rans S-7. ## Similar events ### Rans S-7 rudder cable break in the United States (July 2014) After a prolonged taxi to the active runway, during alignment, the left rudder pedal sank completely and the pilot, who was also the owner of the aircraft, realized that the cable connecting the rudder pedal to the rudder was broken at the same pulley as on 974-GL. That S-7 had 850 flight hours and was equipped with original stainless-steel control cables. During repair work, the pilot discovered that the left aileron cable was also very worn, with several broken wires, at a pulley. He then replaced all control cables with galvanized-steel cables. Since that event, he has performed regular checks of these cables and plans replacement every 800 flight hours. No wear has been noted since. The pilot stated that he had learned of at least three other identical cases on S-7s. ### DHC-6 accident at Moorea on 9 August 2007 Shortly after takeoff, the pilot had lost pitch control of the aircraft after the break of the elevator up-control cable. The investigation had shown that the stainless-steel cable had failed in fatigue following significant wear at a cable guide. The other DHC-6s of the company were equipped with carbon-steel cables, much less sensitive to wear but sensitive to corrosion, particularly in a saline atmosphere. The maintenance organization had nevertheless never observed degradation, whether corrosion or wear, during the annual replacement of the carbon-steel cables. It is also noted that wear is difficult to detect on a cable installed on an aircraft. The BEA had issued eight recommendations following that investigation, including one to the European Union Aviation Safety Agency (EASA) on a review of the design and service experience of other aircraft on which stainless-steel cables are used for primary controls, to determine measures that might appear useful to safety. Following that recommendation, EASA considered that, in view of the actions and investigations conducted during the investigation, this review was not necessary. ### Beechcraft 1900D incident at Lyon on 9 October 2012 During initial climb, the pilot flying noticed that his action on the electric trim compensator command had no effect. The manual trim compensator command did not work either. The crew turned back and landed at their departure aerodrome. On the ground, the trim compensator cable was found broken at the winding around the pulleys of the autopilot servocommand. Examination of the cable showed that half of the wires had broken by overload and the other half by fatigue crack propagation. These damages could not have been detected during planned maintenance. A similar case had already been reported to the manufacturer in September 2006. Following that first case, the manufacturer had neither modified the planned maintenance actions on the cable nor set particular checks or expiration limits for the cable. Following that investigation, the BEA issued a recommendation to the FAA and the manufacturer to make mandatory a modification of the trim compensator system, or, failing that, the replacement at regular intervals of the trim compensator cable, in order to avoid the rupture.