read.fwf in is statement

Question

My data includes different sizes rows for record types. Every format of record types is different. I need to use read.fwf in if statement. I have a basic example below:

filexx <- file.choose()
conn <- file(filexx,open="r")
  linn <-readLines(conn)
  for (i in 1:length(linn)){
  #print(linn[i])
  #print(substr(linn[i], 81, 84)) 
    if (substr(linn[i], 81, 84)=="0461"){
    aa <- read.fwf(file=linn, widths=c(5,5,5,5))
    aa 
 }
    else{
    
    print("#NA")
 }  
    
}
close(conn)

When I have run print(substr(linn[i], 81, 84) row, I receive all record types, but if I have run if clause, I receive just 13 lines of #NA. What is my fault?

Thank you,

I want to parcel the required fields.