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Safe - Immediate turnaround is easy, i.e. according to experience it is possible to reach departure gate quickly and without extra security check when doing same plane turnaround.
Intermediate - Immediate turnaround is doable, but requires e.g. extra security check.
Risky - Immediate turnaround not recommended. (See notes.)

TO KEEP THE WIKI AS COHERENT AS POSSIBLE, PLEASE USE "SAFE", "INTERMEDIATE" OR "RISKY" APPROPRIATELY! (I.e. no "Safe" for stations that require any kind of security or transfer check, not to mention going landside, etc.)

Immediate turnaround information for European AY destinations:

ACE: ?
AGP: Safe (Arrivals pour directly to departure gate.) Details here from August 2022
ALC: Intermediate, Arrivals pour from jetbridge to "funnel pathway" which takes people to baggage claim, but one can look for "Transfer" signage and take escalator up to the gate area. No checkpoints.
AMS: Safe (Arrivals pour directly to departure gate.)
ARN: Safe / Intermediate (Arrivals pour directly to departure gate, except gate 62 arrival pours to baggage claim. ATR flights may be riskier if one ends up with a bus gate.)
ATH: Intermediate at best
AYT: ?
BCN: No direct turnarounds due to operated by IB.
BER: ?
BGO: Safe (Arrivals pour directly to departure gate.)
BLL: ?
BMA: Safe (Transfer door is before going to the terminal exit and boarding will not start before the incoming plane is empty.)
BRU: Safe (Arrivals pour directly to departure gate.)
BUD: Safe (Arrivals pour directly to departure gate.)
CDG: ?
CFU: ?
CHQ: Risky (To landside first and security needed. Long lines possibile.)
CPH: Safe (Arrivals pour directly to departure gate.)
CTA: ?
DBV: ?
DUB: ?
DUS: ?
EDI: ? (Security check required for sure.)
FCO: Intermediate / Risky. Bus transportation can cause long walks.
FNC: Intermediate (Exit via baggage claim and reclear security, but should be doable if you exit among the first from the inbound flight. Mobile BP not available, obtain a BP from HEL.)
FRA: Safe (Even with the bus from stand you can make it.)
FUE: ?
GDN: Risky (Providing it is ATR by Norra, apron position, walking / bussing to the arrivals, queue security (can be very long), sprint upstairs to the gate.)
GOT: Safe / Intermediate(At least on tube arrival, after exit from the tube to the terminal area, turn around and you are at the departure gate. No info on possible bus gates though.)
GVA: ?
GZP: ?
HAJ: Safe (Arrival at departure gate)
HAM: ?
HER: ?
IBZ: ?
INN: Intermediate / Risky (To landside first and then security. No airside transit.)
IVL: Safe, arrivals pour into the gate area.
JOE: Intermediate (Exit via baggage claim and reclear security, but should be doable if you exit among the first from the inbound flight.)
JSI: ?
JTR: ?
JYV: ?
KAJ: ?
KAO: ?
KEF: ?
KEM: ?
KGS: ?
KOK: ?
KRK: Intermediate (AY rarely has a jetty position so bus, arrivals then go upstairs to departures for security, there is a fast track for OW elites - not well signposted - separate B/Pass scanner to the left)
KTT: ?
KUO: Intermediate (Exit via baggage claim and reclear security, but should be doable if you exit among the first from the inbound flight.)
LHR: Intermediate (Need to go via Flight Connections to reclear security, which may take time depending on the time of the day.)
LIS: ?
LIN: Safe, arrivals pour into departures.
LJU: ?
LPA: ?
LYS: ?
MAD: No direct turnarounds due to operated by IB.
MAH: ?
MAN: Intermediate/Risky, requires reclearing security.
MHQ: ?
MSQ: ?
MUC: Safe (Arrivals pour directly to departure gate.)
MXP: Intermediate / Risky (Arrivals come into a different floor, transfer requires walking through a transfer point and distances are quite long.)
NAP: ?
NCE: ?
OSL: Safe / Intermediate (D gates pours directly to departures. E gates also pours to departure gate, follow transit arrow, automatic gate door will open during "normal" hours. IF door doesn't open go upstairs try the transfer security. Very rare reports of stand arrival with bus to exit, but should still be doable, security is usually fast and short distances.)
OUL: Safe (Arrivals pour directly to departure gate.)
PFO: ?
PMI: ?
PRG: Safe (From arrivals walk up to departures to departure gate.)
PVK: ?
RHO: Risky (Arrivals pour to baggage claim, security check usually has long lines before you get to the departure hall.)
RIX: Risky. After deplaning, you walk to the terminal, but boarding is done with buses. My flight was delayed, and they started boarding before the plane was even there.
RMI: ?
RVN: Intermediate (Exit via baggage claim and reclear security, but should be doable if you exit among the first from the inbound flight.)
SPU: ?
SZG: ?
TAY: ?
TFS: ?
TLL: Risky (May have a remote stand arrival, when departing flight has been boarded into a bus with boarding gate already closed.)
TLV: ?
TOS: ?
UME: ?
VAA: Intermediate (Exit via baggage claim and reclear security, but should be doable if you exit among the first from the inbound flight.)
VBY: ?
VCE: ?
VIE: Safe (Arrivals pour directly to departure gate.)
VNO: Risky. (Departing pax board bus when arriving pax still deplaning. Connection corridor available but not sure how straightforward it is).
VRN: ?
WAW: Safe (Arrivals pour to departure gate.)
ZRH: Safe (When exiting the bridge, you are under the gates and there are inclined speedwalks that bring back to the gates upstairs.)

Immediate turnaround information for selected longhaul AY destinations:

DEL: Intermediate (There's plenty of time for the obligatory visit to the transit desk and security. However, you'll need a self-printed visa confirmation to show the gate agent at HEL.)
DOH: ?
DXB: Intermediate (Follow "connections" to security downstairs and after that go to transfer desk if needed.)
JFK: Intermediate (Generous time with the new schedule, but you'll need to clear US immigration so ESTA or visa is needed.)
NRT: Intermediate (OLCI and mobile BP works, no need to go landside. There's transfer security, though.)