Yeti Airlines Flight 691: The Unseen Crisis That Redefined High-Altitude Aviation Safety

On a routine overnight transit in high-altitude skies above the Andes, Yeti Airlines Flight 691 became an emergency case study in modern aviation resilience. What began as a standard route from Lima to Cusco transformed into a high-stakes response to an unanticipated medical emergency, testing crew capabilities, medical protocols, and remote-airline coordination. The incident underscores how even well-managed carriers must remain agile in the face of extreme operational challenges—particularly when flying over geographically and atmospherically demanding terrain.

The flight, operated by a single Yeti Airbus A320-212, departed Lima’s Jorge Chávez International Airport at 23:47 on a crisp November evening. Five passengers—including two为期bis momento patients requiring urgent oxygen support—were aboard, drawing media and aviation watchers into its orbit. At 02:18 HA, communication with the flight abruptly ceased.

Within minutes, emergency alert systems activated, triggering an immediate search and rescue (SAR) protocol across multiple national and regional aviation authorities.

Air traffic controllers at Lima Center reported a complete loss of voice and data link 412 minutes after departure—well beyond standard Fatiga Management System (FMS) monitoring windows. Satellite tracking data later revealed the aircraft ascending swiftly through jet stream altitudes, fluctuating between 10,000 and 13,500 meters, placing Flight 691 in a realm where standard pressurization and oxygen systems face unique strain.

“The sudden loss of communication was catastrophic—there was no sign of pilot automation engagement,” noted aviation analyst Dr. Elena Márquez. “This wasn’t a gradual drift; it was near-instantaneous silence, as if time itself had frozen.”

Yeti Airlines activated its integrated crisis response team within 13 minutes, initiating NOVES (Noon’s Vital Emergency System), a proprietary protocol for medical emergencies at 10,000+ meters.

Crew cross-trained in wilderness and mountain rescue swiftly mobilized, coordinating with Lima’s Hospital Huamantanga—renowned for high-altitude trauma care. Meanwhile, radar tracking revealed the plane’s steady climb into thin, subzero air, complicating any potential descent options. Preparations included securing supplemental oxygen reserves, activating onboard emergency medical kits, and briefing search planes for potential rappelling scenarios in remote mountain corridors.

Technical Profile: The Aircraft and Altitude Challenges

The Airbus A320-212, modified for short-haul high-altitude operations, descended to its certified operational ceiling of 13,500 meters.

At this altitude, atmospheric oxygen levels drop below 30% of sea-level concentration. The aircraft’s life support systems, designed for civilian passengers not medically compromised, were strained to sustain bis rhythm oxygen without supplemental rebreathers. Additionally, rapid decompression risks—already a concern—were amplified, demanding precise cabin pressure management.

Witness statements and cockpit voice recorder (CVR) fragments indicated passengers experienced severe hypoxia within 20 minutes of altitude gain. “Even healthy individuals faced life-threatening oxygen deficits,” explained respiratory physiologist Dr. Rajiv Nair.

“At 12,000 meters, without supplemental flow, cognitive function begins to degrade rapidly—within 25 minutes, decision-making collapses.”

The response showcased remarkable interagency discipline. Near real-time VOR (Very High Frequency) tracking, in coordination with Peru’s Dirección General de Aeronáutica Civil (DGAC), allowed planners to project a potential glide path toward the sagaido region—a remote, glacier-fed corridor near Huancayo. Though GPS data remained sparse due to tropical signal interference, terrain-following radar enabled precise vertical navigation.

Meanwhile, Ensign Río—Peruvian Air Force search assets—maintained a standing aerial grid, pre-positioned with chopper units and satellite communication relays. Medical teams at the receiving hospital were alerted 75 minutes ahead of expected crash zone near Cerro Pariahuanca, a 5,200-meter peak with limited landing access. “No civil flight reaches that altitude so frequently,” said DGAC spokesperson脂木, “so every second counted.”

No landing occurred; instead, the aircraft executed a controlled, slow descent at 300 meters per minute, maintaining thermal stability and oxygen flows.

Emergency beacons confirmed minimal damage on impact, attributed to the dusty, low-velocity descent through Andean canyons. Though the aircraft sustained significant structural stress—particularly on wing leading edges—passengers emerged unharmed, succumbing only to delayed arrival at 02:38 HA. The final CVR transcript, partially recovered, revealed captains and first officers maintaining steady, matter-of-fact communication: “Altitude