Date: 201305
Local time of day: 1201-1800
Location: ZZZZ.Airport, FO
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Citationjet (C525/C526) - CJ I / II / III / IV
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Personal
Flight phase: Takeoff / Launch
ATC / advisory: Tower ZZZZ
Reporter organization: Personal
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Distraction; Confusion; Communication Breakdown
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Flight Deck / Cabin / Aircraft Event Other / Unknown
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Air Traffic Control Separated Traffic; Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: We were given a clearance with routing instructions and then as filed; climb flight level two seven zero; a squawk code; and mach decimal seven zero;' which was read back and confirmed as correct. We taxied out with the Ground Controller and we were then instructed to monitor the Tower. Whilst still some distance from the runway we were cleared to enter and line up; and as we approached the runway we were cleared for take off. Our clearance and brief to this point was a climb to FL270 direct to a waypoint. At approximately 60 knots during the take off we heard the Tower Controller instruct us 'amend clearance level two hundred' which I read back and was not corrected by the Controller. The Captain started to try to reset the altitude preselect; but I noticed he was straying from the centerline of the runway; and I suggested we should wait till we were airborne so he could maintain directional control during the takeoff roll and climb away from the runway. We agreed that I would set the new altitude once we were airborne; and I did so. After takeoff; we were instructed to contact Departure and I made contact stating 'Passing (I believe it was approximately 2;000 feet; but I do not have a written record of this figure) climbing flight level two hundred.' The Controller replied 'recycle squawk' and said something else which was not clear. I read back the squawk and the Captain said he thought the Controller said something about a heading and that I should call her back and check this. At this moment another Controller on this frequency took over from her and instructed us to 'stop climb five thousand feet' and then told us that we had not followed ATC instructions. He then asked for confirmation that we had stopped our climb at 5;000 feet which we informed him that we had. He told us there was traffic ahead and above of us and that we should have been on a heading of two zero zero degrees for our climb. I told him this was not what we had understood from the Tower Controller and apologized.Once the other aircraft had passed us we were cleared to continue our climb; but he informed us that he would have to file a report about this incident. I believe filing a report is the correct thing to do in order to help prevent a repeat of this type of problem; and I am therefore filing this report to present the situation from the flight crew perspective. In my opinion the amendment to our clearance should have been given either prior to the commencement of our take off; or after we were safely airborne. During the takeoff roll our concentration should be fully on the immediate task and the distraction of attempting to make changes to selections at high speed whilst still accelerating for takeoff could lead to an accident. If we did misunderstand the Tower Controller's change to our departure clearance during the takeoff roll; there was still an opportunity for him to correct us when I read back the clearance. Since he did not correct us; there was no reason for us to think we were not carrying out the revised instructions correctly.Both the Captain and I understood the change to be an altitude and not a heading change as he was trying to make changes to the altitude preselect as I was reading back the clearance. When we made contact with the Departure Controller and she could see we were not going in the direction she wanted us to take; I would have thought it should be a priority for her to make us aware of the heading she wanted us to be on - especially if by not doing so we were climbing towards another aircraft. The remainder of the flight was completed without any further problems.




Synopsis: A Cessna CJ3-25B crew mistook ATC's revised heading clearance; given during takeoff; for an altitude change and climbed on a heading not intended or expected by ATC; creating a conflict with another aircraft. The reporter states several missed opportunities for ATC to notice the misunderstandings during the flight crew's read-back of the clearance instructions and particulars.