Leeds Crown Court heard how only fast-thinking by one member of staff at the Leeds-based airline prevented Scott Burns's actions being a "complete disaster" for the company.
Despite that intervention, the company estimated 27-year-old Burns's attack cost it £165,000 in lost business, the court heard.
Jailing Burns, of Morley, for 10 months, Judge Andrew Stubbs QC heard how the motive was revenge because Burns was unhappy about how Jet2 dealt with a disciplinary matter against him relating to an incident at a "roadshow in Benidorm" in 2017.
No further details of the incident were outlined in court.
Judge Stubbs told Burns: "What you intended to do was to cause as much damage to Jet2's computer system as you could.
"But for the prompt measures of an employee of Jet2, this would have been disastrous and brought their computer system crashing down.
"This went far beyond being mischievous. This was a revenge attack for a perceived slight you had suffered."
Judge Stubbs rejected a plea from Michael Walsh, defending, to suspend Burns's sentence.
The judge said he needed to send a message about the "pernicious and far reaching impact" of cyber-crime and to "those who are minded to commit this type of offence".
Prosecutor Rebecca Austin told the court Burns used logins he still had to access the system and delete all user accounts, including those with admin privileges, in January 2018.
She said one quick-thinking IT worker in the firm managed to create a new, hidden admin account as the attack was ongoing and, through this, was able to avert a "complete disaster" and rebuild the accounts from a back-up.
Ms Austin said Burns also accessed the email account of Jet2 chief executive Steve Heapey.
The defendant pleaded guilty to eight counts under the Computer Misuse Act at a previous hearing