Light Transport; Low Wing; 2 Turbojet Eng
Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 30; Flight Crew Total 6000; Flight Crew Type 800
Situational Awareness; Workload; Distraction; Confusion; Communication Breakdown
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance; Flight Crew Took Evasive Action; Flight Crew Became Reoriented; Flight Crew FLC complied w / Automation / Advisory
Human Factors; Procedure; Weather
We were assigned a final vector to join the localizer; told to maintain 2;600 until established and cleared for the ILS 16L into HEF. We presently were at 3;000 and set to join the localizer between GIGEY (cross at 3;000) and DORGE (cross at 2;200). I set 2;600 (or what I recall being 2;600). I told the PF we were 'good to 2;600' and I verified the approach was armed by the PF on the autopilot control panel and verified the annunciation on his PFD. I believe it was about this time he called for Flaps 20. I remember thinking it was a little early for that because of the standard profile for an ILS; but selected Flaps 20 since it was not really an issue to configure early. I think we continued to configure for the approach during this time which means I was running the Before Landing checklist and was distracted with those duties. Potomac Approach contacted us with a low altitude alert showing 1;600 instead of 2;600 and gave the altimeter setting. This was the first time I noticed we were at 1;600 instead of 2;600. I confirmed with Potomac we were indeed at 1;600 and we're going back to 2;600. I selected a higher altitude in the pre-selector (2;300) because we were close to DORGE at that time so we climbed up to capture the glide slope before DORGE. We intercepted the glide slope and landed without further event. One of 2 things occurred: Either I set 1;600 instead of 2;600 or the PF selected 1;600 from the 2;600 I set; not realizing I had already set the altitude. Regardless of how the improper altitude was selected; this can be prevented by both pilots verbally confirming any altitude selections. Though this is our normal procedure; something obviously was missed between the 2 of us and can be prevented by diligent insistence upon both pilots actively confirming altitude changes.
A light jet crew on approach to HEF received an ATC low altitude alert call at 1;600 ft on the Runway 16L ILS before DORGE. The autopilot altitude set had somehow been changed unnoticed from 2;600 ft to 1;600 ft.