The spell-check application of most word processing software programs would not catch a slip-up of these two words. Spell-check is looking for words that aren’t in its dictionary, and words that resemble words in its dictionary but are possibly spelled wrong. Spell-check isn’t perfect. It doesn’t know and can’t guess what word you wanted or what word you meant, it can only judge the words on the page. If you used words that are all spelled correctly, it gives you a pass anyway.
Autocorrect suggests words that start with the same letters. It’s suggesting what word you may want to save time, but quite often, its suggestions are pretty off base. They don’t help you out, but they do make you laugh.
Impending is an adjective. It describes something is highly predicted or bound to happen.
Impeding is the gerund form of the verb impede. It means to holding up, delaying, creating a barrier or obstacle, getting in the way of an activity or goal.
The following story uses both words correctly:
Imran was winning the golf championship with just 4 holes to go, when lightning began to strike several miles away. He knew there was an impending storm headed his way, but he was on such a successful streak. He resented Mother Nature impeding his inevitable win today. What if he didn’t feel as focused and confident tomorrow?