Date: 201404
Local time of day: 0601-1200
Location: EGLL.TRACON, FO
Flight conditions: VMC
Light: Dawn
Aircraft: B777 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B 
ATC / advisory: TRACON EGLL
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Human-Machine Interface; Distraction; Confusion; Communication Breakdown
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Deviation - Altitude Undershoot; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Detector: Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance; Flight Crew Took Evasive Action
Contributing factors: Aircraft; Human Factors; Procedure
Primary problem: Ambiguous

Narrative: The flight was on an assigned heading of 360 degrees; on a right base for Runway 29L at LHR. Autopilot (A/P) was on. We were level at our assigned altitude of 4;000 feet. A few seconds later; we were given an intercept heading of 070 degrees and 'Cleared to intercept the LOC.' I armed the LOC and made the callout to my crew. Shortly thereafter; ATC told us to 'Descend on the glidepath; cleared for the ILS 29L at LHR.' I pushed the APP button to arm the G/S and saw the G/S armed on the FMA. I called this out to my crew and the First Officer said something muffled that I took to mean that he agreed. I heard nothing from the IRO. The LOC broke case and started to come in. I glanced out the window to the one o'clock position to try to visually acquire the runway environment; but the early morning sun was making it difficult to acquire it visually. I glanced down to the FMC to check my distance to the runway but I was distracted to see the G/S was about 1 dot low and dropping. Wanting to acquire the G/S now that the LOC was captured; I temporarily set 1;000 feet in the ALT window and announced 'FLCH' (Flight Level Change). To assist with the descent; I partially deployed some speedbrakes. I made the announcement that we were high and the First Officer asked what altitude we were descending to. I replied that I was descending to the G/S but during this discussion; we were now almost 2 dots low. The First Officer commented he thought we were on a false G/S as the G/S was climbing up again. The IRO said he thought that ATC cleared us to 3;000 feet. I set 3;000 feet in the ALT window as I leveled off and retracted the speedbrakes. To that the First Officer and I replied that we did not hear that clearance. On the LOC at 3;000 feet; (no lower); I disengaged the A/P and hand flew for a few seconds. Now that we were on LOC and properly positioned to intercept the G/S from below; I reengaged the A/P; called out and pushed the APP mode button and confirmed the G/S was armed. Both crewmembers agreed. A few moments later Approach Control turned us over to LHR Tower frequency and tower told us to 'maintain 3;000 feet until G/S was captured; follow the G/S.' A few moments after that; Tower 'cleared us to land Runway 29L LHR.' The A/P flew down the LOC and G/S normally. A 1;000 feet I disengaged the A/P and hand flew the jet to a normal landing.


Second narrative: Pilot flying was the Captain. Pilot monitoring was the First Officer. We were given vectors to join 09L ILS into London. On an intercept path to join the approach we were told to maintain 4;000 feet and follow the G/S inbound. The vectors that were given resulted in use joining the approach outside of the 7.5 DME fix on the approach. To my best recollection we were approximately 12 DME out from the airport. As we were joining the approach the G/S showed we were 1 dot high. At this point I looked down to check the FAF altitude so it could be set and we could correct toward the G/S. The Captain (PF) at this point set the MCP altitude to 1;000 feet; selected Flight Level Change; and put out the speedbrakes. Both changes to the MCP were not verbalized or verified and I had my head down looking at the approach chart. When I looked back up we had not joined the G/S and were at approximately 3;500 feet showing 2 dots low. I verbalized that we were 2 dots low on the G/S and the Captain disconnected the autopilot and leveled at 3;000 feet. Shortly after Approach Control told us to maintain 3;000 feet and follow the G/S inbound. The approach from there was uneventful.


Synopsis: A B777 received an EGLL ATC clearance 'Intercept the Runway 9L Localizer; descend on glideslope' so the Captain engaged APP but because they appeared high on Glideslope he began a FLCH descent to recapture it. The First Officer and IRO realized they were capturing a false glideslope so they leveled and re-intercepted.