Three of four top management executives who moved from Airphil Express to Zest Air in March 2012 have quit the low-cost carrier after a short stint.
Brian Hogan, former chief executive advisor at Zest, and former chief commercial advisor Steve Allen have both moved on to be consultants at Mango Aviation.
Former marketing head Alfredo Herrera has, meanwhile, joined competitor Philippines AirAsia as commercial head.
Only chief financial officer Richard Laig, who moved with the trio to Zest in March 2012, remains at the airline.
The exodus from Zest started sometime in October 2012, say sources.
They add that Hogan, Allen and Herrera felt that "their expectations were not met" and that there were "too many challenges" in their way at Zest.
Sources had earlier told Flightglobal that the four moved from Airphil because of disagreements over the direction the carrier should undertake, especially after the investment by San Miguel.
The owners of Zest have also invited bids from several airlines to buy a stake in it. Cebu Pacific, AirAsia and flag carrier Philippine Airlines are understood to have been approached.
Zest's president and chief executive Alfredo Yao had said in local media reports that Zest-O Corp will remain the controlling stakeholder of the airline, even with the possible entry of new investors.