Flight History
On October 21, 2009, Northwest Airlines (NWA) flight 188, an Airbus A320 (registration N374NW), operated as a regularly scheduled passenger flight under 14 CFR Part 121 from San Diego International Airport (SAN), California, to Minneapolis-St Paul International Airport (MSP), Minnesota. The aircraft departed SAN at approximately 1659 central daylight time. The flight crew consisted of a captain and a first officer, along with three flight attendants and 144 passengers. The captain was the flying pilot.
The takeoff, climb, and initial cruise phases were reported as normal by the flight crew. The planned route programmed into the flight management computer (FMC) was flown during climb and cruise. The aircraft leveled off at flight level 370 (37,000 feet) at about 1822.
Incident Sequence
At 1839, the Albuquerque Air Route Traffic Control Center (ARTCC) completed an automated information transfer (AIT) and radio communications transfer to the first Denver ARTCC controller. NWA188 checked in at 1839:16 and was acknowledged. At approximately 1845:49, the first Denver controller completed an AIT to the second Denver controller and directed NWA188 to contact Denver Center on frequency 134.12 MHz, which the flight acknowledged. At 1846:28, NWA188 checked in with the second Denver controller on frequency 134.12 and was acknowledged.
At about 1856:41, the second Denver controller completed an AIT to the third Denver sector and directed NWA188 to contact Denver Center on 132.17 MHz. After a second directive at 1856:56, NWA188 responded at 1857:01, "okay three two one seven, northwest one eighty eight." This was the last ATC communication from NWA188 while in Denver Center airspace. Flight data recorder (FDR) data showed no radio microphone keying until 2012:46.
NWA188 entered the third Denver sector but did not check in on the assigned frequency. The controller initiated an AIT to the fourth Denver sector. At 1905:31, the oncoming third Denver controller directed NWA188 to contact Denver Center on 127.02 MHz, and again 21 seconds later, but received no response. NWA188 entered the fourth Denver sector without checking in. At about 1912:30, the oncoming fourth Denver controller completed an AIT to the next sector and directed NWA188 to contact Denver Center on 126.32 MHz, with no response. NWA188 entered the fifth Denver sector without checking in.
At about 1924:16, the fifth Denver controller completed an AIT to Minneapolis ARTCC and directed NWA188 to contact Minneapolis Center on 124.87 MHz, repeating at 1924:25, with no response. At 1924:32, the controller called NWA188 for a radio check with no response. The fifth Denver controller then inquired with the first Minneapolis controller if NWA188 had checked in; it had not. The Denver controller stated he would "go find him."
At 1924:55, the fifth Denver controller asked the fourth Denver controller to try to contact NWA188. At 1925:14, the fourth Denver controller made a single transmission asking the flight to contact Denver ARTCC on 126.32 MHz. At 1926:07, the fifth Denver controller contacted the Denver Area 5 front line manager (FLM) to request that NWA dispatch be contacted to direct the pilots to contact Minneapolis Center on 124.87 MHz.
Between 1930 and 1942, multiple attempts were made by Minneapolis controllers, NWA dispatch (via ACARS), and other NWA aircraft to contact NWA188, without success. At 1944, two more ACARS messages were sent. At 1946:56 and 1951:56, the second Minneapolis controller attempted contact. At 1956:40, a transmission on 121.5 MHz directed NWA188 to contact Minneapolis Center on 119.87 MHz.
FDR data indicated that at about 2001, the flight mode annunciator on the pilots' primary flight display reverted from navigation to heading mode. At 2012:46, NWA188 transmitted on frequency 132.125 MHz (Winnipeg Area Control Center, Thunder Bay Low Sector) and advised they had overflown their destination and needed to turn around. The controller directed them to contact Minneapolis Center on 123.72 MHz. At 2014:06, NWA188 established communications with the fifth Minneapolis controller on 123.72 MHz, stating they were distracted and had overflown Minneapolis. The flight was given radar vectors for arrival into MSP and landed without further incident.
Post-Incident Interviews
Flight Crew
Both pilots stated they did not fall asleep during the flight. They reported that the #1 radio was used for ATC communications, the #2 radio was set to 121.50 MHz, and NWA procedure was for the #3 radio to be set to the ACARS frequency. The captain programmed the FMC and entered a standard terminal arrival route for MSP but did not enter an anticipated arrival runway. The pilots removed their headsets and listened to ATC over cockpit speakers; they heard "chatter" but did not recall hearing their call sign.
About 2 hours into the flight, a flight attendant brought meals to the cockpit. The captain left the cockpit for a lavatory break, with the lead flight attendant remaining in the cockpit during his absence. The first officer did not leave the cockpit. After the meal, the pilots began a conversation about the Preferential Bidding System (PBS) for crew scheduling, which had recently been implemented as part of the NWA/Delta merger. Both pilots characterized the system as confusing. The captain retrieved his laptop to show his bid results; the first officer also brought out his laptop and placed it on his tray table. Both laptops were open simultaneously. The first officer tutored the captain on the bidding process for about 15 minutes, according to the captain. Both pilots stated they did not hear any audible alerts or see ACARS message indications on the Electronic Centralized Aircraft Monitor (ECAM) during that time.
The pilots stated their first indication of a problem was when a flight attendant called to inquire about arrival. The captain looked at the multifunction control and display unit (MCDU) and saw no flight plan information; he then saw Duluth to his left and Eau Claire to his right on the navigation display. The first officer immediately contacted ATC, though neither pilot recalled the frequency used. ATC provided a frequency for Minneapolis ARTCC. The first officer then noticed the ACARS message indication on the ECAM and attempted to retrieve the messages.
Flight Attendants
All flight attendants stated the flight was normal from a cabin perspective. The lead flight attendant estimated crew meals were delivered around 1900. Late arrivals were common at MSP due to construction and weather. At about 2015, the aft flight attendant called the cockpit to inquire about landing time for connecting passenger information.
Air Traffic Control
Controllers interviewed described NORDO flights as "common events" occurring several times per shift. Normally, they would contact company dispatch, and pilots would establish contact after receiving an ACARS message. There was no standard procedure for indicating when communication was restored. Several controllers noted that air carrier crews often did not acknowledge frequency changes.
The initial third Denver controller did not remember the event until reviewing the voice tape; he was sequencing traffic and handling a weather diversion when he accepted the AIT. The relieving third Denver controller made two attempts to contact NWA188 but received no acknowledgement; he considered it not unusual. The initial fourth Denver controller had no recollection; recorded data showed he accepted a handoff 2.5 minutes before being relieved. The relieving fourth Denver controller transmitted to NWA188 but assumed the previous controller had already transferred communication.
The Denver Area 5 FLM experienced phone delays contacting NWA dispatch. He did not advise the Denver operations manager in charge (OMIC) or the Minneapolis FLM because he saw the aircraft had been electronically transferred to Minneapolis and assumed communications were restored. He noted that 121.5 MHz was not available in all sectors.
The first Minneapolis controller informed his FLM (Minneapolis Area 5) that NWA188 was NORDO and typed "NORDO" in the data block. The Minneapolis Area 5 FLM called NWA dispatch but did not contact the OMIC, expecting the aircraft to contact ATC shortly. The Minneapolis Area 3 FLM became aware of the situation through overheard transmissions and contacted NWA dispatch; she later informed the OMIC. The acting OMIC noted the NORDO on a notepad but did not use the checklist because he was acting for a short time. The duty Minneapolis OMIC was not aware until the second notification; she then called the Domestic Events Network (DEN) and coordinated regarding a possible fighter intercept, but communication was restored soon after.
Personnel Information
The captain, age 53, held an airline transport pilot certificate with Airbus A320 and Boeing 727 ratings, and a first-class medical certificate dated May 5, 2009, with a near/intermediate vision restriction. He was hired by Republic Airlines (later merged with NWA) on November 18, 1985, and had accumulated 18,641 total hours, with 8,196 as pilot-in-command. In the 90, 30, and 24 hours before the incident, he flew 178.5, 43.6, and 8.2 hours, respectively. His most recent recurrent training and proficiency check was on January 25, 2009.
The first officer, age 54, held an airline transport pilot certificate with Airbus A320 (second-in-command privileges only) and Boeing 727 ratings, and a first-class medical certificate dated September 22, 2009, with a near vision glasses requirement. He was hired by NWA on January 3, 1997, and had accumulated 13,811 total hours, with 5,345 as second-in-command in the A320. In the 90, 30, and 24 hours before the incident, he flew 210.7, 23.2, and 8.2 hours, respectively. His most recent recurrent training was on December 7, 2008.
Both pilots had been off duty for two days before the trip. The incident flight was the second day of a five-day trip sequence, the first time they flew together. They reported normal overnight sleep and felt rested upon departure for the incident leg.
Medical Information
Upon arrival at MSP, airport police administered a field breathalyzer test to both pilots; results were negative. In accordance with 14 CFR Part 121, Appendixes I-J, both pilots submitted to testing for alcohol and five major drugs of abuse; all tests were negative.
Flight Recorders
The aircraft was equipped with an L-3 Communications Fairchild Model F1000 FDR, which was in good condition and data were extracted normally. The cockpit voice recorder (Honeywell model 980-6020-001 SSCVR, 30-minute solid-state) began recording during final approach to MSP. Discernable conversations were related to aircraft operation; no discussions about the NORDO event were recorded. After arrival at the gate, conversations were muffled and difficult to discern.
Additional Information: Northwest/Delta Merger
On April 14, 2008, Delta Air Lines announced its intention to merge with NWA. In September 2008, the FAA approved Delta's plan for interim operations and a single operating certificate transition. In October 2008, NWA became a wholly-owned subsidiary of Delta, with full integration planned by the end of 2010. A joint transition team was created to oversee integration of flight operations. NWA pilots received revised manuals and computer-based training in phases. At the time of the incident, the airline was in phase four of its integration process.
A320 Onboard Communications
The Airbus A320 is equipped with VHF and HF communication systems. The incident flight utilized these systems for ATC communications.