Security officials are frantically trying to discover how a retired long distance trucker accidentally managed to take a fully loaded semi-automatic handgun on to a crowded flight from America's busiest airport.

Blake Alford didn't realize what he had done until he got to his hotel room after his flight from Atlanta to Chicago, but now wants to know how Transportation Security Agency staff let him through security and on to the Southwest Airlines plane.

The incident occurred less than a week after a Russian plane flying out of Egypt was blown out of the sky, killing all 224 people on board. The terrorist group ISIS has claimed responsibility for that attack.

'How could the TSA not have spotted it?' Alford, 67, said in an exclusive interview with Daily Mail Online. 'Especially as it was just a few days after the Russian plane blew up.'

Blake Alford didn't realize what he had done until he got to his hotel room after his flight from Atlanta to Chicago, but now wants to know how Transportation Security Agency staff let him through security and on to the Southwest Airlines plane

'I'm a law abiding citizen, but what if I was someone with terrorist motives?,' asks Alford. 'I have a carry permit — but not for carrying on airplanes.

'I'm a law abiding citizen, but what if I was someone with terrorist motives? I have a carry permit — but not for carrying on airplanes.'

TSA national spokesman Mike England told Daily Mail Online the department is investigating what went wrong. 'When our employees fail to meet standards, we hold them appropriately accountable,' he said.

Alford flew with his girlfriend Lisa Raman and her son on the early-morning flight 314 from Hartsfield-Jackson Airport in Atlanta to Chicago's Midway Airport on Nov. 5. They were traveling to a graduation ceremony.

Just five days earlier, a Metrojet Airbus A-321 had exploded over the Sinai Peninsula, en route from the Egyptian resort of Sharm el-Sheikh to St. Petersburg, Russia. Western experts believe Flight 9268 was brought down by a bomb smuggled on board, although both Russia and Egypt have tried to downplay that theory.

That served as a warning to airports throughout the world, although only inbound international flights to the United States were subjected to increased security. Still officials in Atlanta should have spotted Alford's gun, he says.

It was only when Alford and his party reached their hotel room in Chicago that he realized his Ruger .380 semi-automatic pistol was in his backpack, fully loaded with seven hollow point bullets.

'My immediate thought was "Oh, Mother-of-God, what have I done",' Alford, who lives in Jonesboro, Georgia, 15 miles south of Atlanta, told Daily Mail Online.

Alford said he likes the convenience of the lightweight compact pistol — which is less than six inches long and weighs 9 1/2 oz. — and usually carries it in his back pocket, but a few days earlier, he had put it into his backpack as he was wearing a Halloween costume that wouldn't accommodate it.

'I have a few .45s and some .38s but I try not to go out with a .45 hanging off my side. I like this pistol because I can have it in my back pocket in case anything happens.'

And on the morning of his trip, he crammed his computer and a few other belongings on top of the gun in his backpack, packed a separate suitcase and headed for the airport.

TSA national spokesman Mike England told Daily Mail Online the department is investigating what went wrong. at the Atlanta airport (above). 'When our employees fail to meet standards, we hold them appropriately accountable,' he said

It was only when Alford and his party reached their hotel room in Chicago that he realized his Ruger .380 semi-automatic pistol was in his backpack, fully loaded with seven hollow point bullets

'I'd just forgotten it was there,' he said. 'I travel a fair bit, but I have never done anything like this before.'

Alford normally travels under the TSA's Pre-Check system, which allows trusted travelers to avoid taking laptops and liquids out of their hand luggage, but because he was accompanied, this time he went through the full security for the 1 hour 50 minute trip.

But even with a full scan, he says, TSA officials failed to spot the weapon.

When he got on the plane, he relaxed with his feet on his bag which he stuffed under the seat in front of him for the 591-mile trip. 'The plane was crowded, but not quite full,' he said.

'I normally listen to my iPod, but for some reason I didn't this time. I'm so glad because if I had pulled out my earbuds I would have noticed the gun in my backpack,' Alford said. 'I would have probably freaked out.'

But it was when he got to his hotel and unpacked that the full horror of what he had inadvertently done hit him.

'I said to Lisa: "I've got a gun with me." She said: "A gun? How did that get here? "

'I told her it was in my backpack, and she said: " How did you get it through security? You could have gone to jail for that." I told her: "Not jail, I could have gone to prison."

Actually, the maximum penalty for taking a gun on a plane accidentally is a $11,000 civil fine.

Alford's oversight is just the latest embarrassment for TSA officials at the Atlanta Airport, which handled more than 96 million passengers, last year, far more than any other terminal in the country.

Last December, Delta baggage handler Eugene Harvey was arrested and charged with putting weapons and ammunition on at least 20 flights to New York. He was indicted by a Grand Jury in February after allegedly putting more than 100 guns, many of them loaded, on planes.

Alford flew with his girlfriend Lisa Raman and her son on an early-morning flight 314 from Hartsfield-Jackson Airport in Atlanta to Chicago's Midway Airport on Nov. 5.

The airport said it was increasing security measures in the wake of Harvey's arrest, but they were not enough to detect Alford's gun.

In the first 10 months of the year, TSA says it discovered an average of six firearms every day in carry-on bags— 83 percent of them loaded. That number of 2,447 was a 22 percent increase on last year's figures.

TSA spokesman England said the department is 'investigating this matter to determine what occurred and what steps, if any, need to be taken to ensure that security protocols are executed appropriately.'

He said the agency is looking for videotape of Alford passing through security, but said the X-ray of his baggage is probably not available as they are normally kept for just a couple of days. He said the department should know more by early next week.

'If we find that standard procedures were not adhered to, we will retrain employees as necessary to ensure compliance with standard operating procedures,' England said.

'TSA employs a robust security system involving multiple layers of security, both seen and unseen, to protect the traveling public,' he added.

For the return trip, Alford says he was careful not to make the same mistake. He broke the gun down, putting the pistol in his suit jacket and the magazine in his shoe, both of which he put in his stowed luggage.

'That was in the belly of the plane where no-one could get to it,' he said.