Citation X (C750)
Flight Crew Air Transport Pilot (ATP)
Troubleshooting; Confusion
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance
Flight Crew Became Reoriented; General Maintenance Action
Aircraft; Human Factors; Procedure
We were aware that the nose tires had been changed overnight and did preflight while it was still dark after the line personnel towed the aircraft from the hangar. All appeared normal at the time. During ferry leg; noticed loud medium pitch howling whine from cockpit area. Wasn't sure what to think of it at that time. After landing; inspected most all of nose area; including rubber seals on all windows; as well as gear doors and mechanisms. Opened and resecured nose avionics doors in case they were not properly seated. Noted no abnormal conditions on the nose or the gear doors. During second leg; howling whine remained present. We had narrowed the area down to the cockpit on the first leg. During the second leg we were able to identify that the noise was coming from lower in the cockpit as opposed to higher in the cockpit. On postflight; we looked things over again; to no avail; at first. After getting all the way down on the ground and looking up back behind where the Nose gear strut drag brace connects; we saw that the panel that covers the nose jack point was missing. I suppose I could have done a better preflight; but to be candid; that area is not normally an area that I check.  All the other items that I check in that area are generally visible with my eyes above the level that would have been required to see that panel missing. It is probably that had my eyes passed over that area I would not have even noticed it missing. I was not aware of that jack point location from any of my training. In the past; I've seen tires replaced by rolling one side up on a wooden block to change the other side; so the thought that the aircraft would be jacked had not really crossed my mind. Obviously; there was a breach of procedure on the part of the maintenance crew. This experience will certainly cause me to look for that sort of panel any time there is any kind of maintenance performed on the aircraft I am assigned to in the future.
The crew showed at approximately XA00 L and shortly after the PIC started the night time preflight while I made cabin preparations for departure. Both pilots conducted their final walk-around before flight and found no irregularities. During flight; a slightly higher cockpit ambient noise level was noticed. After landing; the post flight was accomplished and found nothing causing the noise. After the passenger showed; and prior to the next flight; final walk-arounds were again accomplished and nothing irregular discovered. During the flight; the slightly higher ambient noise persisted. So after landing and during the post flight walk-around; we crawled under the airplane and discovered the small forward jack point panel (that is partially obscured from view by the nose gear door and nose gear strut fairings) was missing. The PIC immediately contacted Maintenance and the ACP to report the finding.I never knew that panel was able or needed to be removed for nose tire maintenance and did not know to look there. It would be great for a document to be provided showing the common plates and panels that maintenance would access during repairs so the crews could specifically double check and back up the maintenance professionals after work is completed.
CE750 flight crew noticed a loud medium pitch whine from cockpit area during the first flight of the day; but no discrepancies are found on post flight. The sound is again heard on the second leg and a thorough inspection of the nose wheel well reveals that the jack point cover plate is missing. Maintenance had replaced the nose tires overnight.