Flight crew reported erroneous radar altimeter indication on Captain's side during takeoff resulted in flight management system errors until reaching 9;000 ft. altitude.
Synopsis
Flight crew reported erroneous radar altimeter indication on Captain's side during takeoff resulted in flight management system errors until reaching 9;000 ft. altitude.
Narrative
After rotation from Runway 7L at PHX; the Captain's Radio Altimeter appeared to be frozen at the normal 'on the ground' indication of -4 ft. AGL. As the pitch attitude was increased above ten degrees on initial climb; the tail strike pitch limit indicator appeared in the Heads-up Display (HUD); in addition to the normal TOGA flight director cues. Due to the erroneous Radio Altimeter indication; the preselected pitch and roll modes did not engage automatically on climb out. I cross checked the First Officer's (FO) Radio Altimeter; and it was operating normally. As we climbed through acceleration altitude; the aircraft was still in TOGA mode; and commanding a pitch to maintain V2+20; so I asked the FO to select Level Change; and set the speed bug to flaps up maneuvering speed. We accelerated and retracted flaps on schedule. Approaching SPRKY intersection; the flight director did not command a turn; so I initiated the turn manually to comply with the SID. I suspect the lateral navigation; which was armed before takeoff; had not engaged because the Radar Altimeter was still not indicating the aircraft had left the ground. Approaching our first level off altitude of 9;000 ft.; the flight director command bars operated normally and engaged in altitude hold and lateral navigation. We continued the flight to ZZZ uneventfully; with all flight instrumentation operating normally. We suspected 5G interference affecting the Captain's Radio Altimeter. The FO's Radio Altimeter did not display any anomalies throughout the flight. We flew a visual approach to Runway XXR at ZZZ backed up with the ILS approach; with the HUD in AIII mode; and noted no anomalies with either radio altimeter.Based on my review of the bulletins disseminated by the flight department; I suspect we had an anomaly with the Captain's radio altimeter that may have been caused by 5G interference at PHX. I feel it's important to make these events known in order for contributing factors to be addressed by the parties responsible for the safe implementation of the 5G network.
Second reporter narrative
We were filed for the MRBIL1 departure off of 07L in PHX. The Captain was pilot flying (PF) and I was pilot monitoring (PM). On departure; we were cleaning up the aircraft and as I was finishing the After-Takeoff checklist; the Captain stated that something was wrong with his Radar Altimeter and it was frozen indicating '-4'. We both knew that the Captain was still hand flying the aircraft as he did not turn the associated Autopilot on since we had just departed and therefore he didn't make the 'my aircraft' callout. I was looking at the Captain's Primary Flight Display (PFD) to confirm the anomaly and then I saw on our FMA that LNAV was in standby mode now and heading mode was active. At this time I saw that our LNAV course on the NAV display was indicating a left turn and instead we were now flying over the fix 'SPRKY'. I cannot remember if I or the Captain immediately used heading knob to make the left turn back on course. I remember thinking that it was as if we treated 'SPRKY' as a fly-over not a fly-by waypoint and so it was very brief before we were back on course. ATC did not query us and there was no other aircraft in close proximity to us at that time. We did not disclose to ATC what had occurred. After getting back on course with utilizing heading mode to fly the LNAV route; the aircraft leveled off at I believe our assigned altitude of 9;000 ft. As the altitude captured; the FMC went back into 'normal' mode with LNAV now being active as well as the Radar Altimeter going back to its normal function. No other abnormalities occurred on this flight or the subsequent two flights as we kept this aircraft for our duty day. On the flight to ZZZ the Captain and I discussed what happened and the possibly reasons.The Captain and I discussed that this may have been a 5G issue and thus the Radar Altimeter was affected. However; my (FO) Radar Altimeter did not show any abnormality and was indicating normally. The Captain also saw an unfamiliar indication in the Heads-up Display and looked it up to see what it was; eventually figuring out it was the 'Tail Strike' indication. That is an associated indication with the Radar Altimeter anomaly. The Captain briefed that we would continue the flight and that we both needed heightened awareness on the approach to make sure the Radar Altimeter functioned normally. It did and so we made the same brief departing ZZZ as I was PF now. We made sure to observe both Radar Altimeters were functioning normally and they did. The Captain made the decision that he would complete a report and did not see the need to write up the aircraft since it did not repeat.In the future it is important for us as the crew to be vigilant in monitoring aircraft systems and always understand the details in the anomalies that result with the Radar Altimeter malfunctioning. Especially with the 5G issue still not being fully completed; we as the crew need to be aware that it may happen even though it is supposed to be working correctly at these major airports. Regardless; we as the crew need to always fly the aircraft first and then ensure we are navigating correctly.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.