From flight cancellations to baggage failures, there's a lot that can go wrong with your airline when travelling. To help you out before you book the Air Travel Consumer Report by The US Department of Transportation has ranked US domestic airlines from best to worst. The report reveals the worst airlines based on four categories: flight cancellations, mishandled baggage, overbooked flights and complaints. Read on to find out which airlines are flying high and those that aren't.

One of the worst feelings when travelling is looking up at the departures board and seeing the word "cancelled" next to your flight. Part one of the report looks at the number of flight cancellations for each airline during July 2019 starting with the airlines that cancelled the least flights to the worst offenders. 

Delta was not far behind Allegiant Air, but it's worth noting the carrier has far more scheduled flights with 90,812 in July 2019 alone. Only 0.4% of their services were cancelled. 

If you're travelling through Phoenix, Dallas Fort Worth or Louisville airports you'll know Mesa as American Eagle, while the airline operates as the United Express brand at Washington Dulles and Houston. It saw 3.2% of its 20,122 flights scheduled in July stay on the runway, up on the 1.9% from last year. 

With headquarters in Dayton, Ohio, PSA is a brand owned by American Airlines flying as American Eagle. It saw 3.4% of services cancelled in July, with passengers on 846 flights facing the misery of rebooking. 

A subsidiary of Delta Air Lines, you might know them as Delta Connection, flying around the country from hubs at Atlanta, Detroit, Minneapolis, and New York. Endeavor comes in fourth on our list of the worst cancellation offenders, also with 3.4% of their 22,312 flights staying on the tarmac.

For every 1,000 bags onboard Alaska Airlines's flights, 4.32 had issues that were reported. It's worth noting that Alaska Airlines got 2.1 million items of luggage onto its planes in July 2019 alone.

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Southwest saw 53,660 mishandled baggage reports, slightly higher than the 49,484 in 2018. That means 4.69 bags had issues for every 1,000 handled by the carrier. However, do note the airline dealt with the biggest number of luggage items of any on the list – a staggering 11.4 million bags.

Trusty Hawaiian Airlines is first on the list with the lowest rate of people denied boarding. It saw 0.00 involuntary denied boardings per 10,000 passengers, with nobody turned away. And they handled 5.3 million (presumably happy) customers. 

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In 2018 only 22 people were denied boarding with Delta, but during the same period this year the company has beaten its excellent track record in this area – there was only one person who couldn't board with the airline from January to July 2019.

Southwest Airlines takes the seventh spot with a 0.32 involuntary denied boardings per 10,000 customers, seeing 2,525 passengers unable to take to the skies. Do note that the airline's results were partly caused by the grounding of the Boeing 737 MAX planes, after two flights crashed in October 2018 and March 2019. And Southwest Airlines also handled 79.5 million passengers from January to June 2019, the most of all the airlines in this section of the report. 

Although American didn’t have the highest involuntary denied boarding rate at 0.73 per 10,000 customers, they did turn away 5,022 people, the highest number of all the airlines listed here. However, like Southwest Airlines, it too was affected by the grounding of the Boeing 737 MAX planes which has negatively impacted the results here.

Alaska is next with the second-lowest, only 17 formally logged complaints in total, with 0.50 grievances per 100,000 passengers. Alaska has also seen a slight drop in their complaints from 2018, when they had 24 complaints in total and a rate of 0.70 per 100,000 passengers.

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Delta was still one of the best performers despite 102 gripes. Of these 23 were baggage complaints and 33 were flight issues, with a complaint rate of 0.65 per 100,000 passengers.

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Republic Airways (partner of American, Delta and United) has seen an increase in the rate of complaints, 0.78 per 100,000 passengers in July 2019, higher than the 0.60 figure from 2018. But in reality Republic only had 13 complaints, 12 of them were flight-related.

Mesa (you might know them as American Eagle or United Express) is the eighth worst performer with a 1.37 complaint rate per 100,000 passengers. It was on the receiving end of 19 formal complaints in total in July 2019, the majority (16) were flight issues.

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Envoy Air (part of American Airlines) takes the fourth spot with a complaint rate of 2.42 per 100,000 passengers. It generated 34 complaints, 28 being flight-related and 2 being about over-sales.

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This year Spirit has leapfrogged Frontier to claim the dubious crown of the airline with the highest complaints rate, 3.64 per 100,000 passengers in July 2019. That's a slight increase from the 3.55 in 2018. Spirit saw 117 complaints overall with 20 about boarding issues and 56 over flight problems.

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