Is a failure to appeal from a conviction a collateral attack on a constitutional ground?

[33 Misc.2d 595] 'It would seem clear that a failure to appeal from a conviction does not always save it from collateral attack on a constitutional ground, or indeed on other ground where the court is convinced justice requires a remedy, though sought collaterally. In other words the Great Writ, and section 2255, are not to be imprisoned within an ironclad rule stated in terms of collateral relief not being a substitute for an appeal.'

See also Askins v. United States, 102 U.S.App.D.C. 198, 251 F.2d 909.