Q400
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude
Flight Crew Overcame Equipment Problem
Aircraft
During departure off of 26L; at 1;400 feet on the Georgia 5 departure; aircraft issued an RA calling for 'Descend; Descend'; requiring a descent in VMC conditions. As Pilot Flying; I leveled off the aircraft while talking to the captain; but due to the low altitude I slowly moved the aircraft into a descent (approximately 50fpm).  The MFD showed the target at plus 0.0 and at 0.0 feet above; on top of the aircraft icon.  Transponders were both set on the second unit.  Pilot Monitoring notified tower we had an RA; and the nearest target was 4 miles down range 2;500 feet above us. Tower stated no other observed traffic. During the descent; around 1;100 feet; the RA was still calling descend; and the EGPWS called out 'DON'T SINK'.  I leveled off around 1;000 feet; strongly believing we had an issue with the transponder and after discussing it with the Captain.  The captain switched us to the number 1 transponder and the issue resolved. The transponder was written up upon arrival [at our destination].If we had been in IMC conditions; this could have led to a really nasty situation with no time to react. The RA asked for a 500 fpm descent; and at 1;400 feet there was little time to resolve the issue.  The EGPWS call further made it confusing by calling don't sink when the RA was calling out 'Descend; Descend'.  Needless to say; we didn't comply with the initial expected climbout on the SID.We believe that the transponder interrogated itself; which led to a false RA.  We had just reached acceleration height; so work load was fairly high.  We expected that the RA was valid; however; when looking for traffic; checking the MFD and talking to tower we determined that there was erroneous data being provided to us.
A Q400 First Officer reported receiving a TCAS RA and 'Descend' command shortly after takeoff with no other aircraft in the vicinity. When the crew responded to the 'Descend' command; the EGPWS alarmed with 'Don't Sink'.