What the point had a message "Begin the mission?" when using Stingray interceptor? Is this because it's based on OXCE mechanics and require 2 pilots? Doing mission with 2 people only easy on very small USOs so every time I have to cancel it when sinking enemy USO with it. Have not tried Mako yet, but I think it might have same effect. Bug or feature?
P.S.
Answering myself - "crafts.rul" has string "allowLanding: true" in section STR_STINGER. I'm changing it to "false" to prevent lading with it. But still need answer from Nord because it could be planned or small mistake.
P.P.S.
Well, Stinger could actually land and 2 pilots could do a mission, this kinda weird but OK. In case if this is was designed it need some info in USOpedia regarding that fact. And I've found some hole on 2nd floor of level 1 T'Leth. Look at screenshot.

Save file attached.
P.P.P.S.
Game crashed on 2nd level of T'leth after I went to trap door on right side. Few my aquanauts get zombified. I killed zombies and tentaculat, second tentaculat became unconscious. After I used chainsaw to make hole in wall and after it I got strange invisible enemy mark on tentaculat corpse. I finished the turn and mod crashed. I can't reproduce it now again. Played on Ironman, so reloading game put me on beginning of 2nd level stage. I'm posting screenshot here, save file (I set Ironman mode off there) so you might try experiment yourself. The log file says something about invalid node on map:
[09-11-2020_23-56-50] [INFO] Bad node in RMP file: ROUTES/LEVEL07.RMP Node #1 is outside map boundaries at X:20 Y:4 Z:0. Culling Node.
[09-11-2020_23-56-50] [INFO] Bad node in RMP file: ROUTES/LEVEL07.RMP Node #2 is outside map boundaries at X:20 Y:3 Z:0. Culling Node.
[10-11-2020_00-08-03] [WARN] No free channels available
[10-11-2020_00-08-04] [WARN] No free channels available
[10-11-2020_00-14-18] [FATAL] A fatal error has occurred: Segmentation fault.
[10-11-2020_00-14-18] [FATAL] 0x5a9740 OpenXcom::CrossPlatform::stackTrace(void*)
[10-11-2020_00-14-18] [FATAL] 0x5aa5b0 OpenXcom::CrossPlatform::crashDump(void*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)
[10-11-2020_00-14-18] [FATAL] 0x41c7f0 signalLogger(int)
[10-11-2020_00-14-18] [FATAL] 0x994710 OpenXcom::UfopaediaStartState::think()
[10-11-2020_00-14-18] [FATAL] 0x7ffd6f5cfcc0 _C_specific_handler
[10-11-2020_00-14-18] [FATAL] 0x7ffd6f5e4680 _chkstk
[10-11-2020_00-14-18] [FATAL] 0x7ffd6f543730 RtlWalkFrameChain
[10-11-2020_00-14-18] [FATAL] 0x7ffd6f5e34e0 KiUserExceptionDispatcher
[10-11-2020_00-14-18] [FATAL] 0x934b50 OpenXcom::Tile::getDangerous() const
[10-11-2020_00-14-18] [FATAL] 0x4dd130 OpenXcom::AIModule::validTarget(OpenXcom::BattleUnit*, bool, bool) const
[10-11-2020_00-14-18] [FATAL] 0x4dd350 OpenXcom::AIModule::countKnownTargets() const
[10-11-2020_00-14-18] [FATAL] 0x4e5c70 OpenXcom::AIModule::think(OpenXcom::BattleAction*)
[10-11-2020_00-14-18] [FATAL] 0x4f3ad0 OpenXcom::BattlescapeGame::handleAI(OpenXcom::BattleUnit*)
[10-11-2020_00-14-18] [FATAL] 0x517990 OpenXcom::BattlescapeState::think()
[10-11-2020_00-14-18] [FATAL] 0x5c1720 OpenXcom::Game::run()
[10-11-2020_00-14-18] [FATAL] 0x41c950 SDL_main
[10-11-2020_00-14-18] [FATAL] 0x996240 console_main
[10-11-2020_00-14-18] [FATAL] 0x996360 WinMain
[10-11-2020_00-14-18] [FATAL] ??
[10-11-2020_00-14-18] [FATAL] ??
[10-11-2020_00-14-18] [FATAL] 0x7ffd6f067960 BaseThreadInitThunk
[10-11-2020_00-14-18] [FATAL] 0x7ffd6f5aa250 RtlUserThreadStart
Screenshot to show where it happened, but again you have to try reproduce it yourself may be even in debug mode. If I can do it manually I'll post additional info here.

P.P.P.P.S.
Got it! Save file just before using chainsaw on the wall in front of me. Using it produce the crash.
Another P.S. =)
I don't know T'Leth related it or not but I got strange effects when played 3rd stage of it too. It seems what wearing advanced bionic armor produce very interesting issue: when aquanaut zombified by tentaculat, later, when this zombie killed and another tentaculat hatched the fall zombie corpse could auto revive because of armor health gain effect. Graphically it's missing on the battlefield but if it detected by friendly unit it's shows as invisible enemy. Saving game and reloading it shows live zombie again. But sometimes, not sure what this is chainsaw trigger it could produce the crash while corpse on the floor but already countered as revived.