Date: 201710
Local time of day: 0001-0600
Location: MKK.Airport, HI
Aircraft: Helicopter
Operator: Military
Flight plan: IFR
Mission: Training
Flight phase: Initial Climb
Airspace: Class E HCF
ATC / advisory: TRACON HCF
Second aircraft: Small Transport
Reporter organization: Government
Reporter function: Departure
Reporter qualification: Air Traffic Control Developmental
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic; Air Traffic Control Provided Assistance; Flight Crew Became Reoriented
Contributing factors: Airspace Structure; Procedure; Human Factors
Primary problem: Procedure

Narrative: Aircraft X requested a practice VOR-A approach to MKK and to fly the published missed approach; followed by turns in holding at MKK VORTAC. I coordinated the missed approach assignment and altitude (climbing to 5;000) with MKK Tower and received acknowledgment. Aircraft X was issued the missed approach instructions; cleared for the approach; and switched to MKK Tower around the shoreline of Molokai Island; established inbound on the final approach course.MKK Tower calls for the IFR departure release of Aircraft Y (routing: MKK V8) reference Aircraft X. I issue a Hold For Release (HFR) and discuss it with R3. We agree that when Aircraft X comes back to us on the missed approach; we will assign him to continue outbound on the MKK-030R segment of the published missed approach in order to preserve non-radar separation with Aircraft Y; which will depart on V8. There is more than 45 degrees between the two courses; and the time requirement is waived with the authorization of visual separation to the Tower. I decide not to have MKK Tower issue the revised instructions to Aircraft X to continue on the outbound heading; because of the confusion that may result in having a third party relay the message.I call back MKK Tower; and approve the use of visual separation between Aircraft X and Aircraft Y and the release of Aircraft Y. The MKK Controller replies that they are unable to launch Aircraft Y at this moment; so I issue another HFR. Less than a minute later; with Aircraft X between MKK VORTAC and MKK; the Tower calls again for a release. I issue identical release instructions as before; and ask them to switch Aircraft to our frequency as soon as practical (so that we can issue the revised instructions).At this point I give a relief briefing; and am relieved from the D3 position. The rest of the events occur during the overlap.Aircraft X checks in; and R3 issues instructions to continue outbound on the MKK-030R. The pilot reads back the instructions; and then says at the end that he is proceeding direct to MKK VORTAC. I heard the misinterpretation; and immediately said 'no' to R3. The R3 controller immediately keys up and says 'NEGATIVE' to Aircraft X and issues the correct instructions again.Sometime during this time; Aircraft Y departs. We notice Aircraft X turning back towards MKK VORTAC in violation of the assigned instructions. Aircraft X is somewhere between 3;200 and 4;000; and climbing. R3 issues Aircraft X to turn heading 360; to get the helicopter away from Aircraft Y. When Aircraft Y checks in; R3 issues an interim altitude of 2;000 to separate him from Aircraft X. Aircraft Y is eventually issued 3;000 and then 4;000 once the traffic is no factor.The biggest contributing factor to this incident was the pilot misunderstanding the revised instructions. Pilot training may have been a factor.The published missed approach for the VOR-A to MKK includes a course reversal. This is a dangerous procedure and introduces another aircraft into congested airspace which is used for arrivals to and departures from MKK. The RNAV-B to MKK has a much simpler and safer missed approach procedure.Although the non-radar release was good; some red flags included the participation of a military aircraft; and the possibility that there was pilot training occurring. With those factors in mind; and knowing that a non-standard instruction was about to be issued; it would have been easier to hold and delay Aircraft Y on the ground until we could verify that Aircraft X was complying with all our instructions. Although the hold and delay on the ground method is not very efficient; it is the safest until the procedures are changed.




Synopsis: HCF TRACON Trainee Controller reported a military helicopter did not comply with its missed approach instructions which placed it into conflict with another departure.