Your plane sweeps left-to-right across the skyline, dropping one row lower each pass. Tap to release a bomb — flatten every building with the bombs you are given, then the next, taller city comes.
Tap anywhere to drop a bomb from where the plane is at that instant. The bomb keeps the plane's forward speed and speeds up as it falls, so it lands well to the right of where you released it — about five to six buildings ahead on the first, highest pass, and less every pass as the plane comes down. A bomb that drifts past the right edge comes back in on the left, just like the plane, so every building can be reached at any height. Each bomb removes the top floor of the building it reaches; a bomb that lands on an empty lot is wasted. Up to four bombs can fall at once, at most one every quarter of a second, and you cannot drop while the plane is off-screen between passes.
The plane flies at a steady speed, wraps from the right edge to the left and comes down one row each pass. If it touches a roof, the run ends. Each city also comes with a fixed number of bombs, shown in the top-left corner: one per floor plus a spare supply of 20 in the first city, two fewer in each city after that, never fewer than 4. Run out of bombs with buildings still standing and the run ends too.
Scoring: 10 points per floor, 30 more for each building levelled, and a city bonus when the last floor falls: the city number × (100 + 40 for every pass the plane still had before reaching the ground + 20 for every bomb left). Then the next city appears with the plane back at the top. Cities get taller and the plane gets 8% faster every city with no top speed, so every run ends sooner or later.
Lead the bomb a long way at first. From the first, highest pass a bomb travels about five to six buildings to the right before it lands, about three by the eighth pass, and under one when the plane is just above the roofs. Releasing directly over a building always overshoots. Pick a target, count that many buildings back, and tap as the plane's nose passes there; then shorten the lead a little every pass. Taller buildings need slightly less lead than short ones at the same moment, because the bomb meets their roofs sooner.
Every bomb counts. The spare supply is generous in the first city and shrinks after that, and a bomb on an empty lot or on a building that another bomb is already about to finish is simply gone. Tapping as fast as the four-bomb limit allows empties the supply before the city is flat. Watch where each bomb is going before you send the next one at the same building, and when only a few buildings are left, wait for the release point instead of firing early.
The tallest building sets the clock. The plane comes down one row per pass, so a tall building meets it after fewer passes than a short one, and every floor you remove buys that building one more pass. Bring the towers down to their neighbours' height first, then sweep the rest. Do not forget that the right edge wraps: a bomb dropped near the right side lands on the left-hand buildings, so the first column is no harder to reach than any other.
Speed is worth points too. The city bonus grows by 40 for every pass the plane still had left and 20 for every bomb you did not use, and it is multiplied by the city number. A clean, quick clear of a late city is worth far more than the floors in it, but each new city is taller, the plane is 8% faster and the spare supply is smaller, so the lead you learned last city is already a little short.