ACROSS
1 - Erratic, as a result of abrupt decline, possibly (13) - UNPREDICTABLE*
9 - American chief getting pressure to barter hot cloak (6) - (-h+p)PONCHO
10 - Constituent at home with liberal revolutionary entertains model (8) - {IN}{T}{EGRAL<-}
11 - Cave study (3) - DEN [DD]
12 - Greg initially goes back to a Dubai website for some pop music (6) - {(-g){REG(+g)G}{AE}
13 - Sri goes west in an excursion to the small landing field (8) - {A}{IRS<-}{TRIP}
14 - Ripped apart clothes (stylish measure adopted for alteration) (10) - {RE{FINE}{ME}NT} ?
17 - Visionary overheard by char (4) - SEAR(~seer)
18 - Spare this for an unproductive person in the U.S. (4) - TIRE [DD] From spare tyre(tire) ?
19 - Teacher's pet (not Henry) in trouble with leader (10) - PACESETTER
21 - Sculpture with sleaze seized by enraged Surya (8) - {S{TAT}UARY*} Didn't know this meaning of TAT.
23 - Clear solution (6) - LIQUID [DD]
25 - Business partner hiding in a health resort (3) - SPA [T]
26 - Two-thirds of the constituents are upset with the price per piece (4,4) - UNIT COST
27 - State of matter found in some TVs (6) - PLASMA [DD]
28 - A delicacy peon cooked found in a reference work (13) - ENCYCLOPAEDIA*
DOWN
2 - Tightening this makes the situation even more difficult (5) - NOOSE [CD]
3 - Concierges miss the first training notice (9) - RECOGNISE
4 - Auditor's agent got into debt obtaining a semiconductor device (5) - (~dye){DI}{ODE}(~owed)
5 - Article smuggled in by a company in Gingee's outskirts to make metal money (7) - {CO}{IN}{A}{G}{E}
6 - Irish tart ingredients help with inflammatory disease (9) - ARTHRITIS*
7 - Power of the Left overwhelms my leader Ray (5) - (-m+l)LIGHT
8 - Steer through the opening, following northbound Ivan .. (8) - {NAVI*}{GATE} (Correction - {NAVI<-}{GATE})
15 - .. speaking with date upset by the sound of a bell (8) - {EMIT<-}{TING}(Correction - {EMIT*}{TING})
16 - Soothing loss of resistance related to a respiration phase (9) -
17 - Geometry box member made by processing sequestra (3,6) - SET SQUARE*
20 - Call by street gangster to get formal dinnerware (7) - {CRY}{ST}{AL}
22 - Giant Greek god who goes around Saturn (5) - TITAN [DD]
23 - Listen in to the lecturer lifting a cocoon occupant (3,2) - LAP UP<-
24 - Srini ambivalent towards concealing some metrical feet (5) - IAMBI [T]