Rear airstairs
A few times on 727s , Eastern Air Canada and several time son extremely loud 1-11s . Living in Stockholm and flying round the Nordics on innumerable DC9-MD80s , the latter I really liked flying on. Always the APU noise and for practical reasons SAS Finnair didnt use the airstairs in the many winter months as outside temp at Helsinki could be -30 mid winter . Always something a bit more special using steps , especially open ones for a flight but jetties cannot be beat for bad weather or wayward pax. I suppose the idea was that the rear stairs were invaluable in places like the US where one end of the leg would be JFK or Chicago and the other Topeka Kansas or Jackson Miss which were pretty rudimentary back then and built for Convair 340s and the like.
Re the TRident vs 727 a much discussed story and no doubt the 72 was a much better aircraft but I think once the Trident had actually got of the ground and up in the flight levels it could show its three dinky little Speys to pretty much any other airliner . I remember the captain pointing out how we easily passed a Vc10 from Rome to London (BEA -BOAC rivalry on that route ) and overtaking various DC9 s LHR to ARN back in the 70s . I rather liked the Trident to fly on but of the options in that era and later the MD80s were the best (so long as you sat at the front)