The Indian Ocean tsunami struck on 26 December 2004, and three months later a huge earthquake devastated the island of Nias. For the next four years, McKerrow worked on numerous disaster-relief operations throughout Indonesia, including the significant earthquakes of Benkulu, West Java and West Sumatra in late September 2009. McKerrow—along with Wayne Ulrich, a disaster-relief expert—experimented with an innovative approach to helicopter aerial-grid mapping based on inaccessibility, altitude, and destitution. Through this technique, using New Zealander helicopter pilot Colin Tuck, they paved the way for critical supply routes to be opened and provide urgent food and shelter materials.