15 
A theoretical error analysis‘ (taking into account 36 individual error 
sources) as well as actual in-flight performance tests, indicate that INS system 
errors propagate in such a way that they increase proportionally with flight 
time and that the typical Schuler oscillation (84 mins) is superimposed. 
The total system error can well be approached by a linear function: 
(a) The lateral navigation error and performance when flying a number of 
parallel lines depends on the total flight time. The (standard) lateral 
navigation error can be expressed by the formula: 
m. ^ *m Qo 
where 
my = standard (lateral navigation) error for INS 
Mao = standard (lateral) error of unit weight (flight time 1 hr) 
t = flight time in hours 
The value for ma, Can be expected to be: 2) 
Mg, =i: 20.300: 80) 
(b) The longitudinal navigation error can be expressed by the formula 
m = + 
Mg = So" 
1) see: LTN-51 Technical Description 
2) Performance test for spraying applications have been carried out by the Government 
of Quebec. The flight pattern — as compared to other tests — is most similar to 
these flown in aerial survey. See Ref. 6.1.