Kevin,
Gisborne Runway IS protected by Signals, the CTC panel controlling those Signals is in the Control Tower, the rest of the Napier-Gisborne line was equipped with Single-line Automatic 3-position Colour-light signals (non CTC) until those were superseded by the Track Warrant system about 1991. (The piece of paper, check the box, American way of running trains
without any lineside Signal protection other than points indicators)
The Airport would have been regulated under the The New Zealand National Airways Act 1945 in the past.
All trains both Passenger and Freight were scheduled and knowing those schedules would have been part and parcel of the Airport Controllers work, to be done in conjunction with Train Control in Napier. I would say that there were written Special Instructions regarding these Signals that would have been
required Local Knowledge for Locomotive running staff working out of Gisborne and would have been a part of the Annual Rules & Reg's oral examination.
[
flic.kr]
Since that Line was outside of my area, I wasn't issued with such Working Timetable inserts nor asked questions relating to them either. I did once occupy the Endevour passenger service loco's cab as a rider up and back on a personal trip to Gisborne in the late 80's but other than the novelty of such a crossing I don't remember anything about it.
All in all, nothing left to chance!
Also at Gisborne there are other runways there, only one sealed, the rest grass, the Airport isn't operated at night after 8-30pm from what I've read.
The line south to Napier is now mothballed since the rains washed out the line in several places however there is a preservation group operating steam WA165(one of the original locos in Gisborne) that still runs the line on occasion. [
www.gcvr.org.nz]
The Napier-Gisborne line was one of the last segments of NZR to be built the line was originally started towards the northeast to connect with the Bay of Plenty lines but it wasn't until 1942 the line was completed up from the South. [
en.wikipedia.org]
The only aviation incident involving Gis airport that I could find [
aviation-safety.net]