RELATED: Delta Is Cutting Flights to These 5 Cities, Starting Sept. 5. Pilots representing the two major carriers have issued a new warning that fatigue is soaring among their ranks, and they’re urging the airlines to consider this issue—along with the human mistakes it could trigger—as a safety hazard. “Fatigue, both acute and cumulative, has become Southwest Airlines’ number-one safety threat,” the Southwest Airlines Pilots Association (SWAPA) explained to the airline’s top brass in a widely covered letter, as reported by CNN Business. The pilots cite mass cancellations caused by weather conditions as well as strong demand for air travel—all while the airlines still struggle to recover from the pandemic’s impact on business—as the major sources contributing to the widespread fatigue in the cockpit. In the letter to executives, the union explained that the number of pilots who reported being unable to work because of fatigue spiked massively last fall, including a 600 percent increase in October alone and another “staggering” 330 percent increase just last month, with the dangerous trend on pace to continue. To better understand the conditions pilots face now, consider that passenger numbers are currently about 90 percent where they were at this time in 2019, before the pandemic hit, per Transportation Security Administration (TSA) data reported by CNN Business. According to Bureau of Transportation Statistics data, meanwhile, the major U.S. carriers are still about 3,000 employees short of the staffing levels from the same period.ae0fcc31ae342fd3a1346ebb1f342fcb In the last couple of years, thousands of pilots retired either voluntarily or by aging out of the role when they turned 65 years old. Further, research from by the Regional Airline Association cited by CNN Business says that another 2,000 pilots will hit the mandatory retirement age this year. And these numbers are only expected to balloon in the coming years. RELATED: For more up-to-date travel news delivered straight to your inbox, sign up for our daily newsletter. Southwest acknowledges that staffing is a major issue and has made it a top priority. The carrier hopes to hire 8,000 new employees this year, 40 percent of which will be flight crew members. But SWAPA president Casey Murray says that this step alone won’t solve the enormous problem. “A lot of our delays and issues that we’re having have to do more with scheduling and connecting pilots with airplanes,” he told CNN Business. “It is inefficient scheduling processes that are affecting when we work in a very dynamic environment.” Delta Air Lines pilots are also sounding the alarm—and they’re doing so even louder by holding demonstrations at airports this month as a way to raise awareness. The Air Line Pilots Association (ALPA) wrote in a message to its members last month that COVID-related circumstances had raised “several opportunities for Delta to re-set its broken pilot staffing issue,” as reported by Fox affiliate WSVN. The union message explained that issues are becoming harder and harder to ignore as passengers flock to the skies. “Delta Flight Operations continues to run the operation at red line,” the message to membership read. “So, if it feels like you are working more and seeing less control over your schedule—you are right; you are.” RELATED: Southwest Is Adding Flights to These 3 Major Cities, Starting June 5.