A B747-400 experienced an apparently phantom TCAS RA shortly after takeoff from SFO.
Synopsis
A B747-400 experienced an apparently phantom TCAS RA shortly after takeoff from SFO.
Narrative
At 1;700 we received a climb RA from TCAS. TCAS displayed the target aircraft at our exact position AND altitude. We notified SFO tower and they informed us that there was no traffic in our vicinity. The ra strengthened from a "maintain vertical speed" to an "increase climb" command. The displayed target remained co-located with our aircraft and its displayed altitude remained identical to ours through 2;400 feet. After 2;400 feet the aircraft symbol went away and the ra was terminated. The PNF First Officer had experienced a similar TCAS event previously. It was on a takeoff from 28R. Only his TCAS event commanded a descent. It was also with a co-located target which was displayed at his same altitude. I believe both tcas events were false warnings. ATC had nothing on radar in either instance. Both targets were displayed at the same position and altitude as the aircraft involved. Much discussion among all the crew members raised the question of whether these events could be the result of some radio interference either accidental or purposeful in nature. It would also be interesting to know if it was the same aircraft that was involved. It should also be noted that the pitch commands provided by tcas were slightly different between the Captain and First Officer PFD. The difference was minimal.
Second reporter narrative
This occurred on the climb out on runway centerline at approximately 2200 feet. Looking outside for a target I saw nothing at the 11 to 12 clock position as shown on the ND. 15 to 20 seconds later; TCAS states increase climb. Target is still showing co altitude with our airplane on climb out. i believe this continued until about 2700 feet. I do not recall the TCAS stating clear of conflict; so I am not sure if it said it and target disappeared or whether it was just satisfied and it went away. The target remained co-located throughout the climb yet no airplane was seen. F/O told Oakland ATC we got a TCAS and asked Oakland to verify target. Oakland stated they saw no such target. F/O asked one more time and Oakland stated again they show no target in the area....during the cockpit brief; the F/O specifically stated that just the week prior; he got a TCAS at the end of the runway on climb out the week before; but that one was a descend command; and being at 2000 feet and in the weather; descending toward the Pacific ocean; it had gotten his attention and he thought it important enough to bring it up today; as the pilot briefed the reject and climb out procedures. Shortly after that; we pushed; taxied; took off and got a TCAS at the same location as the F/O stated the week prior.
NASA callback
The Captain advised he had experienced another nearly identical event roughly one week after the reported occurrence. Combined with his First Officer's event; which occurred roughly a week prior; he was of the opinion that external factors may have contributed to the anomalous RAs. His belief was supported by his later understanding that all three events occurred in different aircraft; but at the same location and altitude and; in all cases; ATC was unaware of conflicting traffic. He remarked that the area below the departure airspace is populated with numerous small manufacturing and developmental businesses from which such interference could possibly be generated. He does not recall having written up the events in the AML and is; thus; unaware of what; if any; maintenance investigation may have taken place. Finally; he advised that the First Officer's earlier event produced a 'Descend' RA which; upon responding; resulted in an uncomfortable descent over climbing terrain not far below.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.