Narrative:

I first noticed [aircraft X] depart off sea indicating a westbound departure; approximately 3 to 4 miles south of where the procedure turns to the west; level at 7;000 feet. I asked the departure west controller what [aircraft X] was doing; as he was out of position and still heading south. Departure west said they were unsure; and was having difficulties communicating with [aircraft X]. I attempted contact on my frequency; and did not receive a response. Due to the aircraft approaching higher terrain to the south; I attempted contact on guard (121.5) and did not receive any response or identify as acknowledgement. I called local assist in the tower at sea and asked them to reattempt communication transfer [with aircraft X] and they said they would. After several transmissions on guard and asking all controllers in the TRACON to attempt contact; I overheard departure west ask [aircraft Y] to say position. I told departure west to try to get them to identify to establish positive identity and attempt an immediate climb for terrain. The aircraft tagged as [aircraft X] flashed identify; and we determined this aircraft was actually [aircraft Y] on the summa departure; not [aircraft X]. Departure west issued an immediate climb and issued the correct beacon code; to establish firm radar contact. The assigned codes for [aircraft X] and [aircraft Y] were different by one digit; and [aircraft Y] had mistakenly used the code for [aircraft X].it appears sea tower failed to perform the primary function of ensuring correct radar identification for a sea departure. After looking at a falcon replay of the asde display for sea tower; [aircraft Y] was tagged as [aircraft X] the entire taxi; displayed on asde and tagged up initially as [aircraft X]. Due to the fact that S46 receives no notification of departure sequence or rolling call from sea; if sea does not correct misidentified aircraft S46 has no way of knowing which aircraft is supposed to be calling; and the opportunity for mishandling of aircraft is high. Additionally; because sea requested all departures in south flow be stopped at 7;000 feet; even when not necessary; it presents a situation where a lost communication aircraft may encounter terrain.if this aircraft would have been issued an initial climb to 9;000 feet they would have been above all terrain in S46 airspace. If S46 had some form of rolling call or rundown list; it seems more likely this error would have been caught.

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Original NASA ASRS Text

Title: S46 controller reported a B737 departed on wrong code; data block; nordo; and nearing higher MVA. SEA Tower did not verify correct code with proper aircraft.

Narrative: I first noticed [aircraft X] depart off SEA indicating a westbound departure; approximately 3 to 4 miles south of where the procedure turns to the west; level at 7;000 feet. I asked the Departure West controller what [aircraft X] was doing; as he was out of position and still heading south. Departure West said they were unsure; and was having difficulties communicating with [aircraft X]. I attempted contact on my frequency; and did not receive a response. Due to the aircraft approaching higher terrain to the south; I attempted contact on Guard (121.5) and did not receive any response or IDENT as acknowledgement. I called Local Assist in the Tower at SEA and asked them to reattempt communication transfer [with aircraft X] and they said they would. After several transmissions on Guard and asking all controllers in the TRACON to attempt contact; I overheard Departure West ask [aircraft Y] to say position. I told Departure West to try to get them to IDENT to establish positive identity and attempt an immediate climb for terrain. The aircraft tagged as [aircraft X] flashed IDENT; and we determined this aircraft was actually [aircraft Y] on the SUMMA departure; not [aircraft X]. Departure West issued an immediate climb and issued the correct beacon code; to establish firm radar contact. The assigned codes for [aircraft X] and [aircraft Y] were different by one digit; and [aircraft Y] had mistakenly used the code for [aircraft X].It appears SEA Tower failed to perform the primary function of ensuring correct radar identification for a SEA departure. After looking at a FALCON replay of the ASDE display for SEA Tower; [aircraft Y] was tagged as [aircraft X] the entire taxi; displayed on ASDE and tagged up initially as [aircraft X]. Due to the fact that S46 receives no notification of departure sequence or rolling call from SEA; if SEA does not correct misidentified aircraft S46 has no way of knowing which aircraft is supposed to be calling; and the opportunity for mishandling of aircraft is high. Additionally; because SEA requested all departures in south flow be stopped at 7;000 feet; even when not necessary; it presents a situation where a lost communication aircraft may encounter terrain.If this aircraft would have been issued an initial climb to 9;000 feet they would have been above all terrain in S46 airspace. If S46 had some form of rolling call or rundown list; it seems more likely this error would have been caught.

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.