Air carrier flight crew reported receiving a ground proximity warning during approach that may have been caused by a nearby tower. The flight crew climbed to a safe altitude and ATC issued a new altimeter setting that was significantly different from what they were previously using.
Synopsis
Air carrier flight crew reported receiving a ground proximity warning during approach that may have been caused by a nearby tower. The flight crew climbed to a safe altitude and ATC issued a new altimeter setting that was significantly different from what they were previously using.
Narrative
On vectors to final approach into GRR; received a GPWS 'pull up' event despite being at an assigned altitude and heading. CA immediately complied with the GPWS guidance climbing 1000' higher than assigned and crew notified ATC who informed them the MSA in their area was 2500'; (aircraft was at 3000' at time of GPWS). Prior to final controller (whose sector the GPWS event occurred) crew was given an altimeter setting of 29.94. After GPWS event ATC notified new altimeter was 29.84 which was consistent with ATIS. No altimeter setting was given between these two instances. Due to a large weather system approaching GRR; crew configuration had CA in Radar mode and FO in Terrain mode. Neither visual scans nor terrain mode on the FO side indicated reason for the GPWS warning. Further post-flight review of the ILS 8R approach plate indicated a tower at 1460' in the area near where the GPWS event occurred. This tower was briefed in the CAs approach briefing but it is unclear if this is what the GPWS was warning.ATIS advised altimeter setting at GRR was 29.84 and changing rapidly due to an approaching weather system. Approach Controller issued an altimeter setting of 29.94 which was inconsistent with ATIS but plausible due to the rapidly changing advisory. Ultimately this setting was incorrect and crew did not receive an updated altimeter setting on handoff to final Approach Controller. Crew was complying with all ATC instructions at time of GPWS event.During high workload especially while approaching a know weather system double check with ATC all assigned instructions and altimeter setting. Also; make sure we brief all highest obstacles that could be encountered.
Second reporter narrative
During our approach into GRR; we received a GPWS pull up event. We were level at ATC assigned altitude of 3000 ft. Receiving vectors for the visual approach to Runway 8R. The Captain immediately disengaged the autopilot and began a climb to 4000 ft. As the pilot monitoring I advised ATC that we were climbing to 4000 ft due to the GPWS warning. Shortly after beginning the climb; before reaching 4000 ft the GPWS warning went away. We advised ATC that we were level at 4000 ft. ATC then began to vector us for the ILS to Runway 8R. Due to the storm system close to the field; the Captain was in radar mode and I was in terrain mode. The terrain mode showed no signs of terrain; both the Captain and I were visually scanning for any sign of terrain or obstacles before the GPWS pull up was issued. We had set an altimeter setting of 29.94 that was issued by the previous controller shortly before the ATC handoff. The new controller upon our check in did not issue us a new altimeter setting until advising him that we were responding to the GPWS pull up the new altimeter was 29.84. Upon post flight review of the ILS 8R approach plate; there is a tower that is 1;460 ft. The Captain briefed this during our approach briefing; we are unsure if this was the cause of the GPWS pull up.The ATIS advised us of rapidly dropping pressure due to the storm front approaching the GRR airport. We had the most current ATIS. However; due to the rapidly changing weather; We set the altimeter setting that the Approach Controller issued us. However; this altimeter setting was incorrect upon our next handoff with ATC who never issued us a new altimeter setting. The ATC issued altimeter setting was inconsistent with the ATIS. However; due to the rapidly changing weather we used the altimeter setting assigned by ATC. We replied with all ATC instructions before and after the GPWS Event.It is important to clarify altimeter settings and weather conditions with ATC when approaching an airport that is being affected by bad weather. It's important to brief and understand any possible obstacles and or terrain in the area so that both crew members are aware of a possible GPWS event.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.