Weird airplane problem.

Changing/deleting entries of the kuid-table of a map/session doesn't change/delete the objects used by the map/session. Instead create a dummy, obsoleting the object. Then delete the object from the map, and dont forget to remove the dummy from CM.
A possible dummy for the jet effect:
- create an empty directory (possibly on the desktop)
- create a config.txt in this directory, like this example (might have to use a different mesh-asset kuid and mesh, this is from TS12)
kuid                                    <kuid2:225064:4010880:2>
username                                "Jet Effect DUMMY"
kind                                    "scenery"
trainz-build                            2.9
category-region                         "UK"
category-era                            "2000s"
category-class                          "BC"

    mesh-asset                          <kuid2:523:1384:1>
    mesh                                ""
    auto-create                         1

  0                                     <kuid2:523:1384:1>
- in CM use 'Import content' to import containing this config.txt
- start the surveyor and delete the dummy (an industrial chimney)
- save the map
- in CM remove the dummy

Find out what the asset is ... make a "New Route" ... place the asset on a specific mark (or building) on the route ... practice deleting the asset on the "New Route" ... sometimes editing the trainzoptions file and changing the line numeral to: -surveyorfov=185, will make it able to stand really high straight up, and get a view of the asset. The "Distant Aircraft" asset may require as many as 8 baseboards to get directly overhead of the asset.