Date: 201307
Local time of day: 0001-0600
Location: IAD.Airport, DC
Flight conditions: VMC
Aircraft: B777 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Airspace: Class B IAD
ATC / advisory: Tower IAD
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: Pilot Not Flying; First Officer
Anomaly: ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Executed Go Around / Missed Approach; Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Contributing factors: Procedure; Human Factors
Primary problem: Ambiguous

Narrative: We were vectored to intercept 19L localizer at 4;000 feet outside of IZUMI at 210 knots. Prior to intercept we were again vectored to intercept 19L localizer about 7-8 NM outside of DOMSI at 180 knots. Just before intercept we were told to look for traffic at 10 o'clock and the runway and report either or both. We saw the runway and called it and I thought we were given clearance to land so I armed the approach mode of the autopilot system. We spotted the traffic at our 12 o'clock and about 2-3 NM ahead at 2;100 feet. He was being vectored in front of us for the same runway. We told the ATC we were too close and he replied he only needed 3/10 of a mile separation to make it legal. The autopilot system then captured the glideslope and we started out of 4;000 feet and since the three of us could not agree if we were given the approach clearance we called and asked and we were told to maintain 4;000 feet. I clicked off the autopilot after descending 300-400 feet and got back to 4;000 feet. In the process of correcting my mistake; the airspeed dropped into the low airspeed (yellow bracket) momentarily as I pushed the throttles up. Then ATC gave us a turn to 160 and then back to 220 to intercept the localizer but by this time we were still at 4;000 feet and only 2.5 NM from the outer marker so we called for a go-around. ATC took us out to the east and brought us back into the localizer about 7 NM out for an uneventful approach.


Second narrative: Approximately 5-7 miles from DOMSE on vector to 19L IAD. Cleared to 4;000 feet and join LOC 19L from 250 heading. Cleared heading 210 to join but not cleared for the approach. After 1-2 miles Captain engaged APP mode. As I said; we were not cleared for the APP plane began to descend on glideslope. Told Captain we were not cleared and and I asked ATC to confirm and he said maintain 4;000 feet. At this point Captain climbed back to 4;000. Now 2-3 miles from DOMSE and told to stay 4;000 and reduce to final speed. We configured for landing and noticed 737 go in front for visual 2 miles ahead. Quick discussion of tight spacing and I told ATC as such and needed lower. ATC gave 3;000 feet and turn to 160 heading for spacing. Meanwhile airspeed began to decay and I called SPEED; SPEED; SPEED. Captain; a bit slow; and I reached for throttle but then he pushed up throttle. Speed decay into yellow band and AIRSPEED LOW EICAS. As this occurred; [we] elected to go-around and ATC hesitated; but we began climb and then we were instructed to turn left away from APP to 19L. We thus deviated from ALT from 4;000 feet as Captain thought [we were] cleared for approach and then ATC put 737 in front at an egregious minimal spacing which contributed to workload as it was sudden and terribly close for stabilized approach. We also had airspeed decay that gave EICAS warning.


Synopsis: B777 flight crew describes the circumstances leading up to a go-around during vectors for an ILS to Runway 19L at IAD. A descent is initiated and airspeed gets low due to minimal spacing with the traffic ahead.