2024-04 · NASA ASRS report 2107350
G-150 pilots reported an unstabilized approach and altitude warning from ATC while on final approach. The crew also determined they were low on the approach when breaking out from cloud bases; performed a go around; then returned for a safe landing.
On Day 0; I was pilot in command (PIC) and pilot not flying (PNF) flying the first of a 3-leg day; when I experienced a deviation from the expected vertical flight path on final approach to ZZZ on the RNAV Y XX approach. The weather was 1300' ceiling and 6 miles visibility in haze. The approach minimums are an 1100-ft ceiling and 4 miles visibility.The flight was procedurally normal and uneventful until our final vector to join the approach at 2000' MSL a few miles outside of the FAF at ZZZZZ. The controller asked us to maintain 170 kts to the FAF and cleared us for the approach. I elected to keep the Autopilot coupled for the approach.While in HDG and ALT hold modes; the course centerline had been extended from ZZZZZ for vectors to join; and the appropriate modes armed for the approach (LNAV; VNAV; and APCH buttons selected). All appeared normal. VPATH vertical mode became active slightly before the lateral course needle centered; but I did not perceive this as unusual given that we were only a few miles from ZZZZZ with 500 ft to descend before crossing the fix.At 2 miles prior to ZZZZZ; the vertical mode changed to VGP; which is normal for an FMS-based approach. The waypoint flashed on the Primary Flight Display (PFD); indicating we were about to pass over the fix. I called for gear down and the landing checklist; while reducing power to slow from 170 KIAS to my final approach speed of 124 KIAS. Full flaps were set once the gear was down. My attention was focused upon the configuration and speed change; and I did not note the crossing altitude as I passed the FAF; but both pilots did confirm the FMS was in VGP mode for the final approach; and per normal procedure; the initial missed approach altitude was set in the altitude selector.The airplane exited clouds at 1300 MSL; only 200 feet above DA. My PNF was completing the landing checklist; but I wanted to visually sight Runway XX before the avionics called 'Minimums.' When I looked up I recall two things: 1) I had a difficult time seeing the runway through the haze. There is no approach light system to this runway; but I did sight it after a few seconds. 2) Once I found the runway; I realized that the sight picture didn't seem right. I thought to myself this looks low. I immediately looked back at the flight instruments; but I experienced confusion with the vertical path needle showing full scale HIGH deviation; the exact opposite of what I thought I was seeing visually. The Autopilot had not pitched down excessively to 'chase' the needle; but I realized something had gone wrong with the approach. We were about 600-700' MSL and in visual conditions; but too far from the runway threshold for this altitude. Before I could get the words out of my mouth; the Tower Controller advised us; 'Low altitude alert; Go Around.' I immediately pressed the Go Around button on the yoke; and the flight director cycled modes correctly. We executed the go-around normally; and we were vectored back for the same approach. This second attempt was also flown coupled; this time with no issues. We landed uneventfully from the second approach. I am uncertain as to what might have been overlooked in the FMS legs page when we loaded; briefed; and subsequently attempted to fly this approach; but I cannot dismiss the possibility that I may have missed something.
We were on a flight from ZZZ1 to ZZZ I was the second in command (SIC) and pilot not flying (PNF) for the flight. The flight seemed normal until inside the FAF on the RNAV (GPS) Y XX into ZZZ where we ended up low on the approach and Tower gave us an altitude alert and told us to go around. Prior to top of descent from cruise the pilot in command (PIC) and I decided to get the D-ATIS from ZZZ. The PIC and I were wanting to get everything set up for the approach early du to arriving into busy airspace. The ATIS said the ILS XX was in use; I think the ceiling reported was 700ft. I loaded the ILS XX approach for ZZZ into the FMS and the PIC briefed the approach. The PIC had me accomplish the appropriate checklists on our descent and arrival. which I did. Once we had been told to descend to another step down altitude; ATC advised there was a new ATIS. I received the new D-ATIS at ZZZ; weather had improved to 1300OVC and 6HZ. The RNAV (GPS) Y XX was now in use. The PIC had me load the RNAV (GPS) Y XX into the FMS and had me set into our refs 1100ft for the LNAV/VNAV minimums (we are not WAAS equipped). We then briefed the RNAV (GPS) Y XX approach. Everything seemed to be set up properly. PIC called for; and I accomplished the appropriate checklists for the continued descent and arrival. ATC then began vectoring us for the RNAV approach. The PIC had me extend the centerline off of ZZZZZ (the final approach fix); as we could see we were being vectored to final inside of ZZZZZ1. The PIC said he was planning on flying the approach on Autopilot. The PIC called for Slats/Flaps 12 setting up for the approach. I selected slats and flaps as requested. ATC gave us a turn to intercept final and told us to maintain 2000ft until established; maintain 170kts to ZZZZZ; we were cleared the RNAV (GPS) Y XX approach into ZZZ; and contact Tower. I could see our position seemed to be correct by looking at our moving map on the MFD as well as selecting the approach plate on the MFD and seeing our position. The PIC called for Flaps 20; which I selected and confirmed set. I saw the Autopilot was intercepting the final approach course and the Autopilot was starting us down to 1500ft. I saw 1500ft to the right of my altitude selector showing that that GPS had the correct crossing altitude at ZZZZZ. The PIC asked me to set our minimum of 1100 in the altitude alerter and he had selected approach mode. I contacted Tower and told them we were just outside ZZZZZ inbound on the approach. Tower then cleared us to land. We had intercepted final and crossed ZZZZZ at approximately 1500ft. The PIC advised that VGP was now active; and asked me to set the initial missed approach altitude of 1500ft. The aircraft appeared to be descending normally. I double checked that we were in VGP mode and once confirmed; I set the missed approach altitude to 1500ft. I was starting to see ground directly below and ahead of the aircraft as we were coming out below the cloud bases. The PIC called for gear down and the remainder of the before landing checklist. A couple moments after I called three green and while I was still completing the checklist; ATC advised we appeared to be low; check our altimeters set to 29.91. I checked all 3 altimeters and verified they had in fact been set correctly. I looked out the front and saw the runway; and that we were lower than we should be for the distance. The PIC had already started correcting altitude; then ATC told us to go around; climb to 2000ft; turn right to 270 degrees and contact Departure. PIC called for the Go around checklist which we accomplished. We got vectors around; reloaded the approach and completed the remainder of the flight normally. The PIC stated that after looking for the runway; and getting it in sight; we appeared low; he looked back in and saw the Autopilot was descending us too low for our distance from the runway; he had disconnected the Autopilot and stopped the descent about the time the controller had asked about our altimeter settings. I feel we must have missed something when we originally set up the approach that made the Autopilot think we needed to descend steeper than normal on final.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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