1 0 5 T ranspor tation The fe xibility of being able t o talk t o an y air craf t fy ing o v er head mak es this syst em of communications v er y adv antageous These por table radios ha v e cr ys talcontr olled freq uencies so a great range of freq uencies are a v ailable Each handheld unit usually carries tw o t o fv e dif f erent freq uencies The recommended frequencies t o carr y are 1 225 MHz C ommon air t oair and air t ogr ound gossip freq uency almost alw a ys monit ored b y air craf t 1 2 1 5 MHz EMER GENCY FREQUENCY All air craf t including commer cial fights monit or this freq uency so in an emergency one can call f or help The frequenc y 1 2 1 5 MHz should ne v er be used un l e s s ther e is an ab solu t e emergen cy an d on ly t o call f or help The most popular type of radio syst em is the VHF FM syst em These radios are smaller than the VHF AM se ts and are much easier t o license U nless the pilo t has e xtra hands a v ailable t o hold ont o his o wn por table se t an addi tion must be made t o the air craf ts present a vionics sys t em This syst em is limit ed t o use in air craf t which ha v e the special VHFFM pack age and thus does no t ha v e the fe xibility of the VHF AM syst ems Bo th radio syst ems depending upon the q ualities of the gr ound units ha v e v er y good range and resolution VHFFM is also v er y useful in lineofsight and gr oundt ogr ound communications be tw een feld cre ws When directing pilo t b y radio do no t giv e landing instructions that req uire ackno wledgement as the pilo t will ha v e bo th hands busy