NTSB Factual Report

HISTORY OF FLIGHT

On October 21, 2009, Northwest Airlines (NWA) flight 188, an Airbus A320, N374NW, did not communicate with air traffic control (ATC) for approximately 1 hour 17 minutes. While the flight was NORDO (no radio communications), it flew past its intended destination at cruise altitude of 37,000 feet but landed without further incident after radio communication was reestablished. There were no injuries to the 2 pilots, 3 flight attendants, and 144 passengers onboard. The flight was a regularly scheduled passenger flight operating under 14 Code of Federal Regulations (CFR) Part 121 from San Diego International Airport (SAN), San Diego, California, to Minneapolis-St Paul International/Wold-Chamberlain Airport (MSP), Minneapolis, Minnesota. The airplane departed SAN about 1659 central daylight time. (All times in this report are central daylight time.)

The captain was the flying pilot. According to flight crewmember statements taken after the incident flight, the takeoff, climb, and initial cruise phases of flight were normal. The flight crew indicated that the planned route that was programmed into the flight management computer (FMC) was flown during the climb and cruise portions of the flight.

About 1822, the airplane leveled off at its final cruise altitude of flight level (FL) 370 (37,000 feet).

About 1839, the Albuquerque Air Route Traffic Control Center (ARTCC) radar controller completed an automated information transfer (AIT)—an electronic radar handoff (rather than a transfer using a traditional paper flight progress strip)—and radio communications transfer to the next controller of NWA188: the first Denver ARTCC controller. (Information in the sequence of events is based on the Federal Aviation Administration [FAA] ATC transcripts, unless otherwise indicated. Details on the specific sectors within the ARTCCs can be found in the docket for this accident at www.ntsb.gov.)

At 1839:16, NWA188 checked in with the first Denver controller, and the controller acknowledged.

About 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 megahertz (MHz). (All frequencies are in megahertz.) NWA188 acknowledged the transfer with “three four one two, northwest one eighty eight.”

At 1846:28, NWA188 checked in with the second Denver controller with “Denver center, northwest one eight eight is with you, three seven zero.” The controller acknowledged NWA188’s transmission.

About 1856:41, the second Denver controller completed an AIT to the third Denver sector and radioed, “…one eighty eight contact Denver center, one three two point one seven.”

At 1856:56, the second Denver controller again directed NWA188 to “contact Denver center, one three two point one seven.”

At 1857:01, NWA188 responded, “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 indicate that, after this transmission, there was no radio microphone keying until 2012:46.

NWA188 entered the third Denver sector’s airspace but did not check in on the assigned frequency. The controller initiated an AIT to the fourth Denver sector.

About 1904, the initial third Denver controller was relieved by another controller.

At 1905:31, the oncoming controller in the third Denver sector directed NWA188 to “contact Denver center” on frequency 127.02, the radio frequency for the fourth Denver sector. Twenty-one seconds later, the controller again directed NWA188 to change frequency.

NWA188 entered the fourth Denver sector’s airspace and did not check in on the assigned frequency.

About 1910, the initial fourth Denver controller was relieved by another controller.

About 1912:30, the oncoming fourth Denver controller completed an AIT to the next sector and directed NWA188 to “contact Denver center” on frequency 126.32.

NWA188 entered the fifth Denver sector’s airspace and did not check in on the assigned frequency.

About 1924:16, the fifth Denver controller completed an AIT to Minneapolis ARTCC and directed NWA188 to “contact Minneapolis center” on frequency 124.87. Nine seconds later, the controller repeated the request for a frequency change.

At 1924:32, the fifth Denver controller called NWA188 for a radio check and received no response.

The fifth Denver controller then called the first Minneapolis controller , to inquire if NWA188 had checked in. The Denver controller was advised that the flight crew had not checked in on the assigned frequency. The Denver controller then told the Minneapolis controller that he would “go find him.”

At 1924:55, the fifth Denver controller called the fourth Denver controller and asked that controller to try to contact NWA188.

At 1925:14, the fourth Denver controller made a single radio transmission to NWA188, asking the flight crew to contact Denver ARTCC on frequency 126.32.

At 1926:07, the fifth Denver controller contacted the Denver area 5 front line manager (FLM) and requested that the manager contact NWA company dispatch, ask them to contact NWA188, and direct the NWA188 pilots to contact Minneapolis center on frequency 124.87. The fifth Denver controller then advised the first Minneapolis controller that Denver ARTCC was contacting NWA dispatch and that NWA188 should be back on the frequency in a few minutes.

At 1930:36 and 1936:42, the first Minneapolis controller attempted to contact NWA188.

About 1932 and 1934, NWA dispatch sent NWA188 aircraft communication addressing and reporting system (ACARS) messages requesting that the flight contact ARTCC.

At 1938:15, the first Minneapolis controller advised the next Minneapolis controller that NWA188 was NORDO and executed an AIT. The first Minneapolis controller then directed NWA188 to “contact Minneapolis center” on frequency 119.87.

At 1939:45, the second Minneapolis controller attempted to contact NWA188.

At 1939:55, the second Minneapolis controller asked another NWA aircraft, NWA196, to attempt to contact NWA188 on that sector’s frequency of 119.87.

At 1942:11, NWA196 advised ATC that they had also requested that NWA dispatch ask NWA188 to come up on frequency 119.87.

About 1944, two ACARS messages were sent to NWA188 from NWA dispatch requesting that the pilots contact ARTCC.

At 1946:56, the second Minneapolis controller attempted to contact NWA188.

At 1948:17, the second Minneapolis controller radioed, “northwest one eighty eight uh if you hear Minneapolis center ident.” No ident was observed. At 1951:56, the controller again attempted to contact NWA188.

In between the transmissions to NWA188, the second Minneapolis controller coordinated with controllers from other sectors to advise that NWA188 was NORDO and scheduled to land at MSP. The third Minneapolis controller advised the second controller that he would attempt to contact NWA188 on frequency 121.5.

At 1956:40, the third Minneapolis controller transmitted on 121.5 MHz for NWA188, “contact Minneapolis center” on frequency 119.87.

About 1957, another ACARS message was sent to NWA188 from NWA dispatch.

FDR data indicate that, about 2001, the flight mode annunciator (FMA) on the pilots’ primary flight display (PFD) reverted from navigation mode to heading mode.

At 2003:02, the second Minneapolis controller coordinated with and transferred control of NWA188 to the fourth controller.

About 2007, 2008, and 2011, ACARS messages were sent to NWA188 from NWA dispatch.

At 2007:41 and 2012:47, the fourth Minneapolis controller attempted to contact NWA188.

At 2012:46, NWA188 transmitted on frequency 132.125 and advised that they had overflown their destination and needed to turn around and head for Minneapolis. Although the pilots did not know it at the time, the frequency they used was for Winnipeg Area Control Center (YWG), Thunder Bay Low Sector. After establishing NWA188’s position over Eau Claire, Wisconsin, at FL370, the YWG controller advised NWA188 that it was on the wrong frequency and directed the pilots to contact Minneapolis center on frequency 123.72.

At 2013:02, the fifth Minneapolis controller requested another NWA airplane to attempt to contact NWA188 on frequency 126.23.

At 2014:06, NWA188 established communications with the fifth Minneapolis controller on frequency 123.72.

At 2014:14, NWA188 radioed, “roger, we got distracted and we’ve overflown Minneapolis. We’re overhead Eau Claire and would like to make a one eighty and do arrival from Eau Claire.”

NWA188 was then given radar vectors to begin arrival into MSP. During the descent, Minneapolis ARTCC controllers queried NWA188 several times concerning the cause of the NORDO. Each time, the pilots indicated that they had “cockpit distractions.”

POSTINCIDENT INTERVIEWS

FLIGHT CREW

During postincident interviews, both pilots stated that neither fell asleep during the incident flight. The flight crew stated that the #1 radio was used for ATC communications and the #2 radio was set to the universal emergency frequency 121.50 MHz. (NWA procedure was for the #3 radio to be set to the ACARS frequency.) The captain programmed the FMC and indicated that he had entered a standard terminal arrival route for MSP but did not enter an anticipated arrival runway. The pilots indicated that, during cruise flight, they had removed their headsets and were listening to ATC over the cockpit speakers. Both heard “chatter” on the radio frequencies but did not recall hearing their call sign.

The pilots indicated that, about 2 hours into the flight, a flight attendant brought meals to the cockpit. During that time, the captain left the cockpit for a lavatory break. For security reasons, the lead flight attendant remained in the cockpit throughout the time the captain was absent. The first officer did not leave the cockpit during the flight.

According to pilot interviews, after completing their meals, the pilots began a conversation regarding the current Preferential Bidding System (PBS) for crew scheduling. The Delta Air Lines PBS system had been recently implemented as part of the integration of NWA and Delta Air Lines. Both pilots characterized the system as confusing. They had received and read the manual and been provided training in the new computer-based system. The pilots’ reported that their discussions mainly concerned the captain’s bid results for November. He had not received the bid results he had anticipated, and the results he received required him to commute to MSP more often than in the past. When interviewed, the captain indicated that he pulled out his laptop computer to show the first officer his bid results. The captain stated that, with his laptop out, his view of the PFD was not blocked.

The first officer stated that, after 4 to 5 minutes of conversation, he pulled out his laptop computer and placed it on top of the extendable tray table in front of him. The first officer said that both laptops were out and open at the same time. Both pilots stated that the first officer was tutoring the captain in the bidding system and process. They also stated that they did not hear any audible alerts in the cockpit and did not see any ACARS message indications on the Electronic Centralized Aircraft Monitor (ECAM) during the time they had their laptops out. The captain stated that he believed the conversation regarding the bidding procedures lasted about 15 minutes.

The pilots stated that their first indication of anything unusual with the flight was when they received a call from a flight attendant inquiring about their arrival. The captain said that he then looked down at his multifunction control and display unit (MCDU) and saw that there was no flight plan information depicted. Then, the captain looked at his navigation display and saw Duluth to his left and Eau Claire to his right. The first officer said that he then immediately contacted ATC, but neither pilot could remember what frequency was used. ATC gave them a frequency to use to contact Minneapolis ARTCC. The first officer then noticed the ACARS message indication on the ECAM and attempted to retrieve those messages.

FLIGHT ATTENDANTS

All of the flight attendants indicated that the flight was normal from a cabin perspective. The lead flight attendant thought that the crew meals were delivered around 1900. The flight attendants indicated that late flight arrivals were fairly normal into MSP due to on-going construction and weather delays. About 2015, the aft flight attendant called the cockpit to see when they would be landing so that they could pass the information on to passengers with connecting flights.

AIR TRAFFIC CONTROL

All of the ATC controllers interviewed indicated that NORDO flights were “common events,” and the controllers estimated that such flights occurred several times a shift. The controllers stated that they would normally call company dispatch, and the pilots would then establish contact on the appropriate ATC frequency after receiving an ACARS message. In addition, all interviewed controllers indicated that there was no standard procedure or requirement for indicating when communication with an aircraft was established.

The initial third Denver controller stated that he did not remember the event until he reviewed the voice tape. He indicated that when he accepted the AIT for NWA188 he was sequencing traffic into Phoenix and another airplane was requesting a flightpath diversion due to weather. The controller initiated an early AIT with the fourth Denver sector just before beginning his position relief briefing.

The relieving third Denver controller indicated that, when he received the position relief briefing, NWA188 was in handoff status. After seeing the next controller accept the handoff, the third controller made two attempts to radio the change of frequency to NWA188 but received no acknowledgement. When interviewed, he indicated that it was not unusual for air carrier flights not to acknowledge frequency changes. He also indicated that he would normally use 121.5 MHz to try to contact general aviation airplanes, but would use the company dispatch for air carrier airplanes.

The initial fourth Denver controller stated that he had no recollection of the NWA188 event. He stated that recorded information indicated that he had accepted a handoff about 2 1/2 minutes before being relieved by the next controller. He also said it was common practice for air carrier crews not to acknowledge frequency changes.

The relieving fourth Denver controller stated that she did not remember the event until she reviewed the voice tape. She said that, at the time she accepted control of the sector, she did not know if NWA188 was on her frequency because the aircraft was still within the sector’s boundary. She transmitted to NWA188 asking the flight crew to switch frequencies, but because there was no response, she thought that the previous controller had already transferred communication.

According to the Denver area 5 FLM, it took him a few minutes to contact NWA dispatch after the fifth Denver controller informed him that NWA188 was NORDO due to phone delays. He indicated that he did not advise the Denver operations manager in charge (OMIC) nor the Minneapolis area 5 FLM that NWA188 was NORDO because he saw that the airplane had been electronically transferred to Minneapolis, so he assumed that communications had been restored. Although he indicated that the controllers use 121.5 MHz, it was not available in all sectors.

According to the first Minneapolis controller, after accepting the AIT for NWA188, he informed his FLM (Minneapolis area 5) that NWA188 was still NORDO and that the FLM should contact NWA dispatch. He also typed NORDO in line 4 of the NWA188 ATC data block.

The Minneapolis area 5 FLM then called NWA dispatch. The FLM stated that he did not contact the OMIC to report the NORDO because he expected NWA188 to contact ATC on the proper frequency after he (the FLM) had contacted NWA dispatch, as had happened many other times with NORDO airplanes.

The

NTSB Probable Cause

The flight crew's failure to monitor the airplane’s radio and instruments and the progress of the flight after becoming distracted by conversations and activities unrelated to the operation of the flight.