I've been there before with my P4. Some reason my P4 responded erratically to my flight controls. I tried RTH, switching flight modes to no avail. I went through flight log and was able to narrow search area to 200m radius. Went there with an actual SAR team I volunteer with as practice exercise for "lost child". We canvassed area and were certain about location. It wasn't until we put word I offered 5,000 peso reward ($100 USD) for return. Wouldn't you know, a farmer saw it land, watched us looking for it and didn't say anything until the reward was mentioned.
