Corporate jet flight crew reported descending below the glide slope on approach to FRG when a complex approach procedure added confusion to their approach descent planning.
Synopsis
Corporate jet flight crew reported descending below the glide slope on approach to FRG when a complex approach procedure added confusion to their approach descent planning.
Narrative
During the approach phase of our flight to FRG we were issued the RNAV19 approach into FRG. ATC instructed us to 'descend to 1600 feet; turn to heading 220 to join the final approach course. Maintain 1600 until established. Cleared the RNAV19 at FRG' As the PM I read back the instructions to ATC. The Captain was the PF and initiated the turn but turned too far. The heading we rolled out on would not intercept the final approach course. As I was about to state a correction; ATC advised us we were east of course and to fly heading 240 to re-intercept. I read back the instructions and we turned to heading 240 at the same time the PF initiated a descent to 1400'. The PF seemed to lose situational awareness momentarily. I immediately advised the PF to return to 1600' and that we could not descend yet as we were not established on the final approach course. Once established we crossed the FAF the PF set a descent rate that caused us to go below the glideslope. I repeatedly stated to correct after no correction was made by the PF; I was about to initiate a go-around but we picked up the runway lights and re-established a normal approach and landed uneventfully.
Second reporter narrative
I was PIC/PF of a flight to FRG. I think it is safe to say that our crew; which consisted of myself; the Second In Command (SIC)/PM; and a Mechanic sitting in the jump seat; were on edge; as immediately prior to flying this leg we conducted a return to service flight after unscheduled maintenance. This flight was conducted in VFR conditions; followed by the flight in IFR conditions; without landing in between. Just a few days prior; this same PIC/SIC/aircraft combination had a complete electrical failure which also resulted in a cabin depressurization. This required the Crew to put on oxygen masks and fly an ILS approach in a 'crippled' airplane to an airport which we had not planned to visit.Contract Maintenance determined that a generator replacement would 'solve the problem.' Our mechanic had reviewed the maintenance with the contractors; and was comfortable with potentially returning the aircraft to service after this 'fix.' The plan was for him to ride in the flight deck jump seat; while I kept the electrical synoptic up on the PF (left) side Multi-function Flight Display (MFD) for the entire flight. This would not allow for me to do my usual scans; to include flipping through ALL of the system synoptics; TCAS; etc.; but this was required for all of us to feel comfortable with the aircraft return to service. In general; the return to service checks and subsequent return of the aircraft were satisfactory; with the Mechanic taking occasional pictures of the electrical synoptic throughout the flight; monitoring voltages and amperages off of all the generators. We of course spoke at some length about the electrical system; and noted that the spread in amperages across the engine driven generators appeared a bit wider than we would expect; but that in general the electrical system appeared to be functioning properly.The flight proceeded in a generally normal fashion; keeping in mind everything I have stated above. We expected the RNAV 19 into FRG. Since we were approaching from the west; we had the IAF 'BLINZ' programmed into the FMS. If we had been approaching from the east; we would have had IAF 'ZOSAB' programmed in. We were then 'thrown a curveball' by New York Approach; which instead kept us high; vectored us over the top of the New York Class B; and then descended us down over the Atlantic; south of Long Island. When they eventually turned us north; we were effectively on the extended center line of our intended landing runway; but 20 miles away and on the opposite side from the approach. I wondered out loud if they intended to put us on a right or a left downwind. In the end; they wound up vectoring us on to a relatively tight left downwind; well inside of ZOSAB. We had been above the clouds to this point; descending into them as we configured and descended on the downwind.IAF 'BLINZ' (on the west side) and IAF 'ZOSAB' (on the east side) both feed into IF 'DEBYE.' Outside of DEBYE the minimum altitude is 2000 feet. DEBYE feeds into the FAF 'MOIRE;' which is to be crossed at no less than 1500 feet. I conducted the approach briefing based on the normal/full approach. I told the SIC to expect to set the Altitude Selector (ASEL) 'to the ground' after we passed MOIRE; and that I would use the autopilot to conduct the approach. The SIC's only question was what rate of descent I planned to use while in vertical speed mode; and I replied that I would start out at 700 FPM and adjust from there. We had previously discussed the benefits and hazards of the 'dive-and-drive' method of flying an RNAV approach as opposed to the 'constant descent angle' method; without ever clearly defining which method is the best. That being said; our aircraft does not have an approved VNAV capability; although it does present a Vertical Path Indicator (VPI) 'for reference only;' which does provide some situational awareness relating to glide path and descent slope.I could argue that Approach Control 'set us up for failure' by turning us on to a left base and having us descend to 1600 feet; vectoring us to intercept the final approach course between DEBYE and MOIRE while in the clouds; but I was confident that we had enough positional awareness to 'make it work.' When cleared for the approach we had some 'wobble' as we transitioned from Heading Mode to LNAV Mode; prompting Approach Control to issue another heading (and thus more Mode changes) to make sure we got on the approach course outside of MOIRE. Add in the 'dive and drive' versus 'constant descent angle' debate (do we stay at 1600 or descend NOW to 1500?) and you can see how some confusion could be added to the process.We crossed MOIRE and I initiated a 700 FPM descent. We stayed below the VPI while remaining above the MDA; so in the end it was a 'hybrid' approach. SIC took the initiative to announce 'I am setting the ASEL for the Missed Approach altitude' and did so. We had intermittent ground contact out the side windows; and then broke out of the overcast above the MDA and a bit below the normal glide path. I shallowed the descent and made a normal visual landing.What could I have done differently? More clarity in my briefings would help. Go into more detail about how I plan to fly the approach; specify EXACTLY when I plan to descend to minimum altitudes; and how I plan to use the VPI as a reference. I could also not ALLOW Approach Control to 'set me up for failure.' Instead of accepting vectors onto final and an intercept of the final approach course between the IF and the FAF; I could have said 'unable' and requested to fly the entire approach; ideally from the IAF. In retrospect; this would have made things easier; we could have better compensated for the fact that I had the Electrical Synoptic on my side as opposed to my regular instrument set-up; and would have given us more TIME to analyze what was happening; instead of 'compressing' everything into a much shorter period of time by getting established IMMEDIATELY outside the FAF. If nothing else; I could have directed my SIC/PM to 'extend the line' in the FMS from the FAF to the IF; so that I would have a 'hard target' to get aligned with outside the FAF; as opposed to using mental gymnastics and a combination of Heading and LNAV modes to try to intercept an imaginary line based on 'positional awareness.'
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.