Narrative:

I was the pilot flying; the captain was the pilot monitoring after briefing the approach for 36L; with my concurrence; our approach was changed to 36R and we were issued a vector to intercept the final approach course; though not cleared for the approach I initially misunderstood these instructions and wanted to hit the approach arm button; but captain explained that we should arm the localizer only in order to prevent an erroneous descent before intercepting the glide slope as a consequence of this sound advice; I completely forgot to arm the approach mode when the final controller issued the 'cleared for the ILS 36R' instructions I don't think I heard the approach clearance - as I know I didn't acknowledge it at the time this failure on my part went unrecognized by me; though I could see that we were going above glide slope - after I had put the gear down; slowed down; selected final flaps and was completely configured but was also completely confounded as to why the airplane wasn't descending! I got some guidance from the captain and was descending towards the glide slope but not as quickly as was required to meet the stabilized approach criteria. Around 1;500 feet AGL; the captain announced that he had the airplane; clicked off the autopilot and descended towards the glide slope at around 1;200feet AGL; we simultaneously broke out of the clouds in to VMC conditions and passed through the glide slope while the captain re-engaged the autopilot; rearmed the approach mode and offered me the flight controls with the runway in sight; I took control of the airplane and leveled off as we were slightly below the VASI; and at the same time; the control tower announced that we were below glide slope and they had a low altitude alert on our approach. I then flew the VASI glide slope indications to a normal; uneventful landing we talked/debriefed at the gate; and I've had some time to reflect on what I did/didn't do what I learned and will do from now on; is to announce out loud as soon as I am confused I thought the approach mode was engaged and would have sworn to it! My experience level wasn't enough to see my mistake and correct it before the captain had to intervene ultimately; I'm certain we were safe and had the option to go around and I will chalk this approach lesson up to one that I can learn from but not repeat! When in doubt of your own actions or the actions of your fellow crew members: say so out loud! Never hesitate to speak up when your comfort level has been exceeded.

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Original NASA ASRS Text

Title: B777 flight crew describes an un-stabilized approach caused in part by fatigue and very low time in the seat by the First Officer and the Captain allowing the First Officer to get a little too far behind before taking over.

Narrative: I was the pilot flying; the Captain was the pilot monitoring After briefing the approach for 36L; with my concurrence; our approach was changed to 36R and we were issued a vector to intercept the Final Approach course; though not cleared for the approach I initially misunderstood these instructions and wanted to hit the approach arm button; but Captain explained that we should arm the Localizer only in order to prevent an erroneous descent before intercepting the glide slope As a consequence of this sound advice; I completely forgot to arm the Approach mode when the Final Controller issued the 'Cleared for the ILS 36R' instructions I don't think I heard the approach clearance - as I know I didn't acknowledge it at the time This failure on my part went unrecognized by me; though I could see that we were going above glide slope - after I had put the gear down; slowed down; selected final flaps and was completely configured but was also completely confounded as to why the airplane wasn't descending! I got some guidance from the Captain and was descending towards the glide slope but not as quickly as was required to meet the stabilized approach criteria. Around 1;500 feet AGL; the Captain announced that he had the airplane; clicked off the autopilot and descended towards the glide slope At around 1;200feet AGL; we simultaneously broke out of the clouds in to VMC conditions and passed through the glide slope while the Captain re-engaged the Autopilot; rearmed the Approach mode and offered me the flight controls With the runway in sight; I took control of the airplane and leveled off as we were slightly below the VASI; and at the same time; the Control Tower announced that we were below glide slope and they had a low altitude alert on our approach. I then flew the VASI glide slope indications to a normal; uneventful landing We talked/debriefed at the gate; and I've had some time to reflect on what I did/didn't do What I learned and will do from now on; is to announce out loud as soon as I am confused I thought the Approach Mode was engaged and would have sworn to it! My experience level wasn't enough to see my mistake and correct it before the Captain had to intervene Ultimately; I'm certain we were safe and had the option to go around and I will chalk this approach lesson up to one that I can learn from but not repeat! When in doubt of your own actions or the actions of your fellow crew members: say so out loud! Never hesitate to speak up when your comfort level has been exceeded.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.