The question involves identifying a genetic disorder that is not inherited in an autosomal recessive manner. Let's explore the inheritance patterns for each option presented:

1. Phenylketonuria (PKU): This is an autosomal recessive disorder. It occurs due to mutations in the gene responsible for breaking down the amino acid phenylalanine. Individuals must inherit two copies of the mutated gene, one from each parent, to develop the condition.
2. Galactosaemia: This is also an autosomal recessive disorder. It results from mutations in genes involved in the conversion of galactose to glucose. Affected individuals inherit two faulty genes.
3. Achondroplasia: This condition is not inherited as an autosomal recessive disorder. Instead, it is an autosomal dominant disorder, meaning that only one copy of the altered gene is enough to cause the condition. Achondroplasia is a common cause of dwarfism and involves mutations in the FGFR3 gene.
4. Wilson's disease: This is an autosomal recessive disorder that affects copper metabolism. It requires two defective copies of the responsible gene for the disease to manifest.

The correct answer is Achondroplasia, as it is inherited in an autosomal dominant manner, not autosomal recessive like the other conditions listed.