How common are emergency landings for airliners? Is there really more than one per day at Heathrow? I've just found an article on one of Italy's most popular newspapers, the "Corriere della Sera", which states that emergency landings are far more common than is normally believed: according to it, at Heathrow there's at least one emergency landing per day. I find this number incredibly high. Is that true?

The article (which is more a collection of "quick facts") doesn't specify the source. I've turned to Google for further info, and the only result I've found is an article by The Telegrpah, which states that the average at Heathrow is slightly above one per week. Even assuming the Corriere journalist wanted to report that figure but got confused and accidentally wrote one per day instead of one per week, it still sounds very high.

An article on abc7ny.com (no idea how reputable that site is) mentions 66 emergency landings at JFK, 50 at Newark and 34 at LaGuardia over a 20-weeks span, from February to June of 2011.

On the other hand, the answers to these two questions on Quora indicate that emergency landings are very rare.

So, if we only consider airliners, how common are emergency landings really?

As pointed out by UnrecognizedFallingObject in a comment, it depends on what is meant by "emergency landing". Is there a commonly accepted definition? If not, since we have to draw a line, I'd say a Mayday counts for sure, and I'd also include a Pan-Pan. Below that, I think we can ignore it.
No, there isn't more than one emergency landing at Heathrow per day

The UK Air Accident Investigation Board (AAIB) defines serious (reportable) incidents in Appendix A of this document.  If we assume that an 'emergency' landing is one caused by one of the incidents in the list, then we can examine the AAIB reports to determine the number of emergency landings at Heathrow (the site supports filters).

I could only find three incidents reported at Heathrow in 2015:


27 July 2015 Airbus A320-232, G-EUYE - In flight fumes
5 February 2015 Airbus A330-323, N273AY - Collided with airbridge 
6 March 2015 Boeing 777-236, G-RAES - Air turnback due to flight crew feeling unwell


Only two of these involved an 'emergency' landing.  2015 may not be a typical year, but a cursory check of the reports for 2014 and 2016 to-date suggests that there are very few incidents.

If you want to get a feel for the number of airline incidents and accidents each day, take a look at AVHerald (you might want to make a contribution to Simon's running costs).  That site reports 29 landings at Heathrow after accidents or incidents, of varying seriousness.  You'll see that, of the thousands of flights each day, there aren't that many problems reported.