Date: 201511
Local time of day: 0601-1200
Location: BFI.Airport, WA
Flight conditions: IMC
Light: Dawn
Aircraft: B767-300 and 300 ER
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Initial Approach
Airspace: Class D BFI
ATC / advisory: Tower BFI
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Fatigue; Confusion
Second reporter function: Pilot Not Flying; First Officer
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; Flight Crew Executed Go Around / Missed Approach
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: On ILS 13R at BFI (11-1 page) G/S and LOC captured (in IMC). At approximately 1900 ft; inside ISOGE we get a line through GS; AUTO PILOT light. Aircraft loses the GS and basically waffles in air. No chance of reintercepting GS. We decide to go-around; execute our procedures and inform ATC. ATC tells us to descend to 1500 ft and track LOC. We elect to level off. In GA mode and a heavy 767 didn't think it prudent to enter a descent to 1500. ATC gives climb and vectors. Points out traffic which we acknowledge. Second approach was uneventful. During second approach; we asked ATC MAP instructions in case it happened again and they told us to descend to 1500 and track LOC. After landing told to call SEA TRACON. TRACON got our story. Also told us we're expected to descend on the GA to 1500 ft due to traffic going into SeaTac. TRACON described it as a 'very unusual procedure'. He also told us there was conflict with another aircraft. The causal factor in this incident is the Missed Approach Procedure for 13R. Nowhere in the procedure does it tell you to descend to 1500 ft especially 7 miles from the airport. I have never heard of a MAP procedure that requires you to descend on a go-around. So even if the descent was published; not sure that is the safest way to do a MAP. TRACON described it as a 'very unusual procedure' but nowhere is there any info highlighting or describing the procedure and the reason for it. In addition; we were also in the 13th hour of duty. We diverted earlier because of weather.


Second narrative: We were cleared for the ILS 13R approach; at 1900 ft MSL the GS failed; yellow line through GS. The autopilot leveled off; we decided to execute a missed approach. GA aircraft starts to climb. I call BFI tower report go around; they say descend to 1500ft; I say what? They say call SEA center. I call Center; they give us a turn 040 climb 3000. Vectors back to ILS. We called Center on the ground they were mad; they said we needed to descend to 1500ft on missed approach. We are not taught to descend on missed approach procedures. This is a very dangerous approach. Something needs to change.


Synopsis: B767-300 flight crew reported confusion on a missed approach at BFI when ATC expected them to descend rather than climb.