The phrase "about to pass through" is correct and usable in written English.
It can be used to indicate that someone or something is on the verge of entering or moving through a particular place or situation.
Example: "The train is about to pass through the tunnel, so please remain seated until we are safely out."
Alternatives: "on the verge of entering" or "nearly passing through".
They chewed their lips and grimaced, fearing that once more both she and them were about to pass through the emotional wringer and sag into a weak, watery, and lifeless heap.
By 7 47 a.m, the train was travelling at 79 mph and about to pass through the crossing in downtown Mebane, NC.
The 5 14 is about to pass through... .. pic.twitter.com/bJEPJeLmIA.
The organizers expect about 2,000 people a day to pass through for lessons and to hear the salsa star Jose Alberto, who is known as El Canario, and the legendary Venezuelan vocalist and composer Oscar D'Leon.
Voyager 1, the fastest and farthest of the interplanetary space probes currently exiting the Solar System, will reach the Oort cloud in about 300 years and would take about 30,000 years to pass through it.
It costs 15 yuan, about $2, to pass through the metal green-mesh fence.
Despite the recession, about 15,000 people continue to pass through Mr. Jones's clubs each night, he said.
Cells needed about 4 d to pass through the halocline and into the upper layer.
Organizers expect about 70,000 people to pass through the main Grand Palais exhibition over the next five days to see some of the world's top galleries and works by the hottest names in contemporary art like Ai Weiwei's "Iron Tree," at a height of 6.28 meters, or 20.6 feet.
Drivers must slow to about five miles per hour to pass through the tollbooth, a limitation not of the technology, but of the old toll plazas.
Now Pakistan has to build about 800km.That it has to pass through the insurgency-ridden province of Balochistan is only one cause for doubting its completion.
