Flight Crew Air Transport Pilot (ATP)
Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Manuals
The Elevator trim on the Excel/XLS has a Nose Up; and a Nose Down limit; or 'stop'; just as the aileron and rudder trim have a left and right stop indicator. The range of the elevator trim; indicated by a white arc on the center pedestal; should be clearly marked when rigged properly. This is typically accomplished with grey paint on the plastic trim covering the unused portion of the white arc at the stops. When checking the elevator trim travel on pre-flight inspection; the elevator trim pointer should fully traverse between the nose up and nose down limits; and not go over. If the travel is not proper; there are several possible reasons. The elevator trim could be out of rig; the trim indicator may be out of adjustment or jumped its track; or the elevator trim is not properly rigged. It is also possible that nothing is wrong with the rigging; but the elevator trim indicator was simply not marked after the elevator trim was rigged; or the elevator trim markings have become worn; and it is no longer possible to determine where the nose up and nose down limits are. When picking up an airplane for the first time; if the elevator trim indicator will not traverse the full range of the white arc; or it is not marked properly; it may be impossible to tell which condition you have; only that something is not right. The first time I encountered this situation; I picked up an airplane that had the elevator trim rigged the night before by maintenance. While checking the elevator trim in the Nose Down position; the pointer stopped unusually short of the end of the white arc; and I queried maintenance about it. The maintenance controller confirmed that it was just rigged the night before; but if I was not comfortable with it; they would have it checked again. As it turned out; the elevator trim was NOT rigged properly; and needed to be rigged again. Since then; I have written numerous squawks on aircraft with this condition. I don't delight in doing so; but there doesn't seem to be clear enough guidance on what is proper; and what is not. I have been given many explanations; including that the white arc doesn't really mean anything; the white arc is simply to provide contrast with the pointer (which is also white); and that the elevator trim markings are not an exact science. I have even seen a maintenance corrective action indicating 'no defects noted'; but the nose up and nose down limits on the pedestal were re-marked with grey paint anyway. This begs the question; if there were no defects noted; why was the pedestal re-marked? Most of the time; however; the corrective action has been to check the elevator trim rigging; and re-mark the elevator trim index; usually with grey paint. As mentioned above; one condition that may be encountered; is where the elevator trim will stop short of the Nose Down limit; and go past the Nose Up limit. I have been told by Maintenance Control that this condition usually means that the elevator trim cable has jumped the track on the manual trim wheel; and needs to be reset. The elevator trim cables jumping the track; or getting caught between the grooves on the inside of the elevator trim; causing binding of the elevator trim; is not uncommon; and has been the subject of increased emphasis during preflight inspection in the past. My personal practice is to check the trim prior to every flight; and not just on the first flight of the day; as I have had this situation occur between flights. The CE-560XL/XLS Maintenance Manual provides some guidance on the issue in section 27-90-30; Elevator Trim Travel Checks. The maintenance manual shows a picture of how the elevator trim indicator should be marked; in chapter 27-32-01; Figure 201. Although it appears to be common practice to set the Nose Up and Nose Down limits by blocking out the unused band of the white arc with grey paint; it is my understanding that there is no specific step in the procedural text of the Maintenance manual to do so.In recent conversations with one of our Non-Routine Flight Operations (NRFO) pilots on the issue; he was in agreement that the trim should traverse fully between the Nose up; and Nose Down limits; and not go over. He also warned of a more hazardous condition that may occur. While operating with the autopilot on; when going from Flaps Zero to Flaps 7 or 15; the autopilot will attempt to trim towards the Nose Down position. If there is insufficient trim authority in the nose down position; the autopilot can no longer compensate; and will disengage; resulting in a nose-up pitch upset. The only way of determining on preflight inspection if the elevator trim has full range of authority is to run the trim the full range from its nose up to nose down position. Without a proper marking of the nose up and nose down limits; or 'stops'; it is impossible to determine proper trim range. The NRFO pilot I talked to also informed me that there have been several instances of elevator trim cables rubbing on something under the floorboards beneath the center console; and there has been at least one case of the cable snapping in flight. This has resulted; apparently; in additional inspections; and replacing of rudder trim cables on phase inspections. While replacing the cables is encouraging news; it also highlights the importance of having the trim cables rigged and marked properly; as well as the importance of pre-flight operational checks. The purpose of this [report] is to bring attention to the issue of the elevator trim on the XL/XLS; and to seek standardization for maintenance; as well as guidance for flight crews on what to look for when conducting a pre-flight inspection of the elevator trim. For maintenance; I recommend that if there is no specific step to mark the elevator trim; after rigging; or after a rigging check; that one be added. It seems to be common practice to paint the unused portion of the white arc with grey paint; but the maintenance manual could use further clarification. This would also standardize the practice; and lead to less squawks when implemented fleet-wide. For flight crews; I suggest a Memo informing pilots of the current elevator trim issues in the fleet; how the elevator trim should be marked; and proper pre-flight procedures; to ensure the elevator trim works properly; and traverses throughout the full range of operation.
The Reporter stated the biggest issue with the elevator trim is that sometimes it will trim too far nose down and not enough nose up or vise-versa according to the indication on the pedestal in the cockpit.The Reporter stated that this is only a seven passenger airplane and weight and balance is very sensitive especially when they are flying at a high altitude (ie 43000 feet) and a passenger or flight crew in moving about the aircraft the elevator trim is constantly working. The Reporter also stated when they were on the ILS using the autopilot; when lowering the flaps the elevator trimmed the aircraft nose down to compensate the lowering of the flaps; if the elevator trim was not rigged correctly it would have tripped off the autopilot pitching the aircraft upward. The Reporter stated that when maintenance accomplishes a rigging procedure for the elevator trim system; they may need to repaint the indication stripe on the pedestal in the cockpit. This in not always accomplished because it is not stated in the maintenance manual to do so.The Reporter stated that often when the elevator trim indication is in the take-off position; and when the throttles are pushed forward for take-off they get a 'Take-off' warning indicating that the elevator trim is not set. This indicates that the elevator trim is not set correctly or not rigged correctly of has an issue with the cables and pulleys.The Reporter stated that after talking with his Chief Pilot and other pilots that this is a constant problem with this type of aircraft.
Cessna Model Citation Excel/XLS Captain reported the rigging procedures for the Elevator Trim system were unclear and inconsistent. The 'Nose-up/Nose-down' limits were unclear while accomplishing their preflight checks.