B737-800 flight crew reported receiving low altitude and glide slope warnings during approach. Flight crew climbed back to correct altitude and continued approach to landing.
Synopsis
B737-800 flight crew reported receiving low altitude and glide slope warnings during approach. Flight crew climbed back to correct altitude and continued approach to landing.
Narrative
After being cleared direct to the IAF for the ILS Z XXR around ZZZZZ (ZZZZZ1 X STAR) I was a little high on the path and selected LVL CHANGE to get back to the path. While slowing and configuring to configure early prior to the IAF; I failed to go back into VNAV. As I crossed ZZZZZ2 (IAF) it looked like I crossed just a bit low which had me scratching my head because the Flight Director (FD) was centered (I did not verify the Flight Mode Annunciator (FMA)... of course it would because I was in VNAV SPD). Somewhere in this area; I assumed I was in VNAV and on the PATH so I selected the approach mins (7600') since I was planning to select the ILS after rolling out on final due to -7 note. Passing ZZZZZ3 as I rolled out on final; I realized I was below the FAF altitude and started to analyze. As I rolled out I got the 1000' call out & GLIDE SLOPE WARNING... I thought I recalled hearing 'ALTITUDE' in the aircraft. I immediately disconnected the Autopilot and brought my nose up to stop the descent and climb back toward the FAF alt. I recaptured the glidepath and made an uneventful landing. Felt like I was stable by 500'. EFB replay showed some deviation below 500 and a long landing. Hindsight... while it didn't feel rushed; a go-around was probably in order.Cause: Desire to expedite back to path and configure early while feeling a bit overconfident how well everything was going at the time; led to a moment of complacency where I failed to return to VNAV. In addition; failure to verify and monitor the FMA resulted in losing track of my Autopilot mode. Trying to find the runway in the haze prior to making the turn to final also played a role in me missing my Autopilot state. BL: No excuse. A touch of complacency had cascading effects.Suggestions: Embarrassingly; it is really about the basics and not getting complacent. Automation management is key. The FMA will tell you what it's doing. Also; when something doesn't seem right; it probably isn't. I should have been more deliberate in monitoring the crossing altitudes. I also should have verified VNAV... VNAV PATH... Cleared for the approach prior to setting the altitude window.
Second reporter narrative
Flying the RNAV to XXR; we are on the arc to intercept the ILS XXR. Approximately; 10 miles from the runway as we are intercepting centerline; we have no raw data for the ILS which is unusual for ZZZZ. I'm checking our frequency's I look back at my display; the magenta triangle is ~ 340 feet below the RNAV path; I look for ILS raw data (none seen); the I saw we are at 135 kts.; 20 kts. slow for our configuration. I said add power; First Officer (FO) added max power; then I command nose down to increase speed. ILS data came in shortly after. We were stable on glide path 1.5 miles from the final app fixCause: As pilot monitoring (PM); I should have been more concerned about the RNAV arrival and not so much about the ILS raw data.Suggestions: Concentrate on the RNAV; don't worry about the ILS data. If the weather has poor visibility; go around via RNAV approach minimums…with no ILS I should have said.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.