ctap_loess.default: no visible global function definition for
  ‘loess.control’
lines.spec: no visible global function definition for ‘plot’
pgram_compare.amt: no visible global function definition for ‘as.ts’
pgram_compare.amt: no visible global function definition for
  ‘frequency’
pgram_compare.amt: no visible global function definition for
  ‘spec.pgram’
pgram_compare.amt: no visible global function definition for ‘par’
pgram_compare.amt: no visible global function definition for ‘layout’
pgram_compare.amt: no visible global function definition for ‘plot’
pgram_compare.amt: no visible global function definition for ‘lines’
pgram_compare.amt: no visible global function definition for ‘legend’
pgram_compare.amt: no visible global function definition for ‘mtext’
pgram_compare.amt: no visible global function definition for ‘acf’
pgram_compare.amt: no visible global function definition for ‘title’
pilot_spec.default: no visible global function definition for ‘var’
pilot_spec.default: no visible global function definition for ‘par’
pilot_spec.default: no visible global function definition for ‘mtext’
pilot_spec.default: no visible global function definition for ‘legend’
pilot_spec.ts: no visible global function definition for ‘is.ts’
pilot_spec.ts: no visible global function definition for ‘frequency’
prewhiten.default: no visible global function definition for ‘ts’
prewhiten.ts: no visible global function definition for ‘is.ts’
prewhiten.ts: no visible global function definition for ‘frequency’
prewhiten.ts: no visible global function definition for ‘start’
prewhiten.ts : NAFUN: no visible global function definition for ‘is.ts’
prewhiten.ts : NAFUN: no visible global function definition for ‘as.ts’
prewhiten.ts: no visible global function definition for ‘lm’
prewhiten.ts: no visible global function definition for ‘residuals’
prewhiten.ts: no visible global function definition for ‘par’
prewhiten.ts : PANELFUN: no visible global function definition for
  ‘lines’
prewhiten.ts : PANELFUN: no visible global function definition for
  ‘abline’
prewhiten.ts: no visible global function definition for ‘mtext’
print.tapers: no visible global function definition for ‘head’
print.tapers: no visible global function definition for ‘tail’
psdcore.default: no visible global function definition for ‘is.ts’
psdcore.default: no visible global function definition for ‘ts’
pspectrum.ts: no visible global function definition for ‘frequency’
spec_confint.default: no visible global function definition for
  ‘pchisq’
spec_confint.default: no visible global function definition for
  ‘qchisq’
splineGrad.default: no visible global function definition for ‘par’
splineGrad.default: no visible global function definition for ‘plot’
splineGrad.default: no visible global function definition for ‘lines’
Undefined global functions or variables:
  abline acf as.ts frequency head is.ts layout legend lines lm
  loess.control mtext par pchisq plot qchisq residuals spec.pgram start
  tail title ts var
Consider adding
  importFrom("graphics", "abline", "layout", "legend", "lines", "mtext",
             "par", "plot", "title")
  importFrom("stats", "acf", "as.ts", "frequency", "is.ts", "lm",
             "loess.control", "pchisq", "qchisq", "residuals",
             "spec.pgram", "start", "ts", "var")
  importFrom("utils", "head", "tail")
to your NAMESPACE file.