The phrase "a challenging task when" is correct and usable in written English.
It can be used to introduce a situation or condition that makes a task difficult.
Example: "Completing the project on time is a challenging task when team members are frequently unavailable."
Alternatives: "a difficult task when" or "a tough job when".
A challenging task when applying high-order digital modulation schemes is the complexity of the detector.
Modeling of physical systems may be a challenging task when it requires solving large sets of numerical equations.
However, assessing factors' influences remains often a challenging task when dealing with hundreds to thousands of correlated variables, whereas only a limited number of samples is available.
The solution of optimal control problems (OCPs) becomes a challenging task when the analyzed system includes non-convex, non-differentiable, or equation-free models in the set of constraints.
Spinetta says the success of UAV missions depends on keeping operators alert — a challenging task when missions can run for months at a time without a day of rest.
It's not that you can congratulate yourself on the skillful execution of a challenging task when all you've had to do is to measure the correct quantity of ground coffee and press a few buttons in the right sequence.
Inferring a scenario of inversions is known to be a very challenging task when analyzing a sequence with relatively few markers and many inversions as in the case of the XY chromosomes.
This is a very challenging task when the industry has a strong interest in using as little space and as little time as possible per animal.
In Rochester, workers at the Lincoln Branch Toy Library, a pioneer among the roughly 300 toy libraries across the country, keep tabs on thousands of board game parts, a particularly challenging task when summer day camps descend.
Acoustic data collection for automatic speech recognition (ASR) purposes is a particularly challenging task when working with under-resourced languages, many of which are found in the developing world.
Breeding for improvement of fruit flavor is a very challenging task when using classical breeding methods due to the difficulty of scoring and quantifying such a complex trait.
