Commercial Fixed Wing
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 9
Human-Machine Interface; Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Chart Or Publication; Human Factors
This is the second pilot deviation I have been involved in in the exact same location and altitude in two months' time. Aircraft X had been cleared to maintain 6;000 and direct to BOJID to resume the BOJID2 Arrival STAR. The aircraft was observed descending through 5;300 between the waypoints BOJID and HIFAL. The flight crew misread; as had happened before; the 4;000 Expect altitude charted at FERUS and began their descent as if they were issued a 'descend via' instruction and as if the FERUS altitude was a requirement and not informational only. Remove all 'expect' altitudes and speeds from this STAR.
Due to short flight time I briefed the PHL arrival on the ground as part of the departure brief. In the briefings I briefed expected altitudes as expected altitude; and briefed that were loaded in the box. We De-iced in ZZZ and then took off. Prior to descent I re-briefed the arrival and the expected altitudes and that they were loaded into the box. On the arrival at BUNTS and at 8;000 feet; ATC vectored is off the arrival to a 030 heading. They then descended us to 6;000 and at 7;000 feet direct BOJID intersection to resume the arrival. We had previously briefed and loaded in the box all expect altitudes on the arrival including the expect 4;000 feet at FERUS. At BOJID we mistakenly started down to meet the 4;000 restriction at FERUS. Approaching 5;000 feet Approach told us to level at 5;000 and informed us of our mistake. Landed 27R with no further incidents. Our mistake was to think the altitude at FERUS was a hard altitude; and that we were cleared to descend via the arrival. A contributing factor to the incident is that KPHL is not an airport that neither I nor the copilot normally flies into. Human error treating an expected altitude like a hard altitude. Altitude awareness on expected altitudes.
PHL Controller and flight crew reported altitude deviation during descent on the BOJID2 STAR.