Date: 201811
Local time of day: 1801-2400
Location: ZZZ.Airport, IL
Flight conditions: IMC
Weather elements / visibility: Snow
Light: Night
Aircraft: EMB-505 / Phenom 300
Flight plan: IFR
Flight phase: Landing
Airspace: Class C ZZZ
ATC / advisory: Tower ZZZ
Second aircraft: Citation II S2/Bravo (C550)
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness
Anomaly: ATC Issue All Types; Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Incursion Runway
Detector: Person Air Traffic Control
When detected: Other after event
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: Heavy snow falling and lots of snow accumulating Runway XX in use. Shortly before this time I had received a call from TRACON saying Aircraft X was minimum fuel and was having vertical and horizontal problems and was asked if the runway was clear enough to land on. I was working Ground and Local combined and had a CIC in the back. I asked the 2 guys working on the runway trying to clear it off for the 2 IFR aircraft; Aircraft Y and Aircraft Z that were proposed to come in behind Aircraft X if the runway was clear enough to bring him in. [They] said to give them 10 minutes and it would be. Based on where Aircraft X was I told TRACON that we could take him. I then told [people working on runway] that Aircraft X is coming in and that they can work till the he was 5 miles out to try to clear as much of the runway as they could for them. Aircraft X was inbound about 5 miles out and; I had told Aircraft X that I had them working on the runway trying to clear as much of it as they could for him. I told [people working on the runway] the aircraft was 5 miles out and to exit the runway and report when clear; since the snow was so thick I could hardly see the 2 plows on the runway I had them report clear. I was told [one] was going to A5 and would report clear and [the other] was going to Runway YY the off runway. [The first] reported clear and then I asked [the other person] again to report clear. [He] told me he was stuck but he was off the runway; close but clear. I then told Aircraft X that the plow had slipped off the runway close but clear around Runway YY on the left side of his Runway and even asked if he was comfortable with that. Aircraft X said he was and landed safely. Behind Aircraft X was Aircraft Y who told me he was having moderate rime ice from 3;000 feet and needed to land. I informed him about the plow that was stuck on the left side of the runway close but clear and asked him if he was OK with it. He told me 'I need to land' so I cleared him to land. After Aircraft Y landed I seen Aircraft Z on the screen coming in on the ILS Runway XX when he was inbound I told him about the plow that was stuck and asked him if he was OK with it and he said it was fine. What led to the event is the CIC did 2 reports for the plow that was stuck and the emergency Aircraft X. My supervisor told me today that I had 3 deals because the plow that got stuck was in the RSA [Runway Safety Area] and since he was stuck that he is an obstacle. We have many charts upstairs and not a single one of them defines the RSA on them; nor does are SOP define the RSA. Inform other controllers that if a vehicle gets stuck close but clear he is now and obstacle; also define the RSA that is not defined anywhere.




Synopsis: Local Controller reported three aircraft to landed with a snowplow was stuck off the runway in the RSA area.