Why didn't Judge Dredd receive any aircraft backup after their 10-24 call?

Question

After Ma-Ma's clan machine guns Peach Trees so bad that some bullets penetrate the concrete and exit the building, Dredd blows a hole in the wall so he and Rookie Anderson get out of the building, on a high floor (50-something?), near a skating rink.

Even though they were aware that the blast shields had cut off their comms, it takes them a few precious minutes to realize that now comms should work, but eventually Dredd does call for backup and mentions they've been under fire and can't maintain their position.

Why does the backup only include 2 judges apparently arriving on foot? Why no aircraft, given their precarious position up there, or at least a van? This was the famous Judge Dredd asking for backup, not any random judge, so he was both important, and in a dire enough situation to ask for backup (in the beginning of the movie, the Justice Hall operator asks him, "Do you require backup?" and proudly answers "No"; but not this time).

Answer 1

I don't think there is a perfect answer to this question without some speculation.

First possible factor: Limit of resources - Dredd: "Twelve serious crimes reported every minute. Seventeen thousand per day. We can respond to around six percent." It's stated early in the movie that crime to response ratio is way out of proportion. We can extrapolate those numbers to indicate that the Judges are stretched extremely thin. Maybe the two judges that show up at the entrance to Peach Trees is all that could be diverted for backup?

Second possible factor: Lack of information -

Anderson: "Comms are back on."

Dredd: "Control. Do you copy?"

Control "Affirmative."

Dredd "10-24 on my GPS. Request immediate assistance."

Control: "Copy, 10-24. Judges under fire. Showing your location as Peach Trees, Sector 13. Confirm."

Dredd: "Confirm. Be advised, blast door defenses have been triggered."

Control: "Can you hold your current GPS?"

Dredd: "Negative. If they come for us, we've got nowhere to go."

Control: "Copy that. Backup is on its way. Just stay alive."

Dredd: "We gotta go back in."

The fact is Dredd doesn't give much information for Control to use. Dredd clearly states that the blast doors are active, but doesn't say there is a breach in the blast doors on their level. He also can't hold his position, so despite control knowing his location, they also know his location is compromised. Controls best option is to dispatch whoever is available to try to open the lockdown from the ground level.

Dredd also doesn't specify how well armed or how outnumbered he and Anderson are, so it's up to control to make a judgement on how much backup is required.

With the points above; an Airship either wasn't available, or wasn't deemed necessary by control.