Solution to 22A has been deliberately left unsolved and is to be answered by a non-regular/novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
Open for anyone to answer, if not solved by 1 PM.
ACROSS
1 Had returned in disarray - kept gunners hidden, undetected (5,3,5) UNDER THE RADAR {HAD+RETURNED}* over {RA}
10 Imprisoned leader disposed of as he was indisposed (5) AILED jAILED
11 Flow rate on board can be solved (9) TREATABLE {RATE}*{TABLE}
12 Find out why active retired men run away (9) DETERMINE {rETIRED+MEN}*
13 Initially some study and leave (5) SCRAM {Some}{CRAM}
14 Moors' short reply to catch a thief in Delhi (7) ANCHORS {AN{CHOR}Swer}
16 Fancy marketing mantra adopted by a group (7) SUSPECT {S{USP}ECT}
18 A recluse accepts money and distributes it among the poor (7) ALMONER {A}{L{M}ONER} Semi&lit
20 Operator's tool to climb over parking line (7) SCALPEL {SCAL{P}E}{L}
22 Manage to get initial guarantee from bank (5) R?D?E (Addendum - RIDGE {RID{Gu...e}E} - See comments)
26 Operation was successful initially on family corruption (4,5) SKIN GRAFT {Su...l}{KIN}{GRAFT}
27 Leaders in Masjids are mainly selected to lead the prayers (5) IMAMS Acrostic Semi&lit
28 Possibly repairing core of the old airmail system (7,6) CARRIER PIGEON*
DOWN
2 Belonging to a family of the languages spoken in Egypt, nothing pertains to the ear (7) NILOTIC {NIL}{OTIC}
3 Deride angrily and admit it keeps you warm (9) EIDERDOWN {DERIDE}*{OWN}
4 Model suit tailored for one in Kigali, perhaps... (5) TUTSI {T}{SUIT}*
5 ...besides eating balanced square meal (9) ELEVENSES {EL{EVEN}SE}{S}
6 Wagers earlier in Spain (5) ANTES {ANTE}{S}
8 Help lift car up and down - others get a heart attack (7,6) CARDIAC ARREST {CAR}{AID<=}{CAR}{REST}
9 Worried old-timers got a medical specialist (13) DERMATOLOGIST*
15 Over time psychiatrist gets depreciation (9) SHRINKAGE {AGE}<=>{SHRINK}
17 Bird takes time - that's astonishing (9) STARTLING {S{TAR{T}LING}
19 Admire a bubbly wine (7) MADEIRA*
23 Keen to get inside a German university (5) EAGER [T]
25 Misbehave with law, having state support (3,2) ACT UP {ACT}{UP}
Reference List
Gunners = RA(Royal Artillery), Run = R, Thief in Hindi = CHOR, Marketing mantra = USP, Money = M, Parking = P, Line = L, New = N, Model = T, Square = S, Spain = S, Time = T