UKH

My boss is wishing to make an ascent of Ben Nevis in December with a group of colleagues to celebrate his retirement.

I have a fair bit of mountain experience and am confident with navigation in poor visibility. We are all fit and healthy as required for our jobs and a few of us are competent in the mountains in summer conditions. Is this just a bad idea? Are the main paths usable without crampons? Any advice appreciated. 

December is most definitely winter on Ben Nevis, chance of driving rain and/or snow, low cloud, strong winds. The days are short and the snow is usually soft and unhelpful meaning slow progress, starting and finishing in the dark is probably likely. Hiring equipment locally isn't expensive and December is quiet for the shops around town so will have a full range of kit but obviously that means you need to know how to use it. 

If in any doubt, get in touch with a local guide or seek out some advice closer to the time and don't be worried about calling it off last second. Plenty other nice hills in the area that will be below the snow line!

December is Winter. There'll probably be snow on the top. Some parts of the main Pony Track path are likely to be icy, especially higher-up. Could be very cold and/or windy.

I'd say walking crampons are definitely necessary at that time of year. Axes might not be necessary if you're sticking to the path, but at a minimum trekking poles (for stability) should be carried. Personally I'd definitely take walking crampons, axe, and poles and recommend you do the same.

Up and down the Ben is a long day out. In December you've got limited daylight, so everyone needs a headtorch, spare batteries, and should be comfortable walking in the dark. Obviously also appropriate clothing, food, flask, etc. Fitness to be on the hill all day.

You need to be able to navigate a dogleg route from the top of the track to the summit cairn. Easy enough in good conditions, but harder in the dark or in limited visibility. See https://www.ukhillwalking.com/articles/skills/navigating_on_and_off_ben_nev....

Some people tend to underestimate Ben Nevis because it's so near to a large-ish town and has a car park at the bottom. It's a serious mountain at any time of year. Have a fun challenge but be realistic and know when to turn back. Only you know your abilities.

Well done for checking this out before someone has an accident!  Nathan's advice is sound especially given that some of your party don't even have summer experience.  You'll definitely all need to be carrying axes and crampons and know how to use them.  The suggestion to hire an instructor (there are lots of good ones in the area) is also good because it means the group will learn the skills they need to be safe as well as getting up into the hills.  Hope you manage to get something worked out.

Plus the instructor will have a cache of kit they can borrow and avoid hiring or one off purchases. The cost overall is likely to be pretty similar, but they'll gain the instruction and overall safety. 

I'd say the same thing I said about this when someone else asked a very similar question a couple of years ago: https://www.ukhillwalking.com/forums/hilltalk/ben_nevis_advice_-_crampons-6512...

Granted, he was talking about October not December, but the jist of the thread is probably applicable, if you add a healthy pinch of extra caution for going deeper into winter.