This Editionâs ILAHFFT entries are taken from our US NASA ASRS[1] sister organisationâs CALLBACK publication Issue 537(October 2024) that highlights some misunderstandings, expectation bias, complacency and problems with overly complex message formats from CPDLC. CPDLC is a great tool, but crews need to use it with care to ensure that the entire message is understood, and controllers need to be clear in their messages and not send rapid-fire CPDLC messages that crews might not be able to process in a timely manner as they attend to other flying tasks. For information, UK CAA are currently considering whether CPDLC will be mandated in UK airspace as a way of reducing R/T complexity and the number of calls.
Reread if You Reroute
â ATC issued a revised clearance via CPDLC. Clearance was, âLoad new route to LEV. Rest of route unchanged.â Free text stated, âGLADZ.LEV…/IAH.â I did not notice the route portion of the message because it was so short, and thought the clearance was only to proceed direct to ZZZ. The First Officer did not notice the error either and programmed the FMC for direct LEV with abeams as I directed, without GLADZ. ATC noticed we had turned to LEV and not GLADZ, and asked if we were proceeding direct to LEV. He stated that he must not have sent the message correctly and then verbally cleared us direct to LEV. I believe he was trying to be kind and let us off the hook. In seeing the CPDLC message, âLoad new route to LEV,â I simply assumed it was to go just direct LEV and failed to read all of the message, and used the LOAD prompt to load the FMC from the CPDLC clearance. I wanted to manually program the FMC with the direct [route] in order to utilize the âabeam waypointsâ function. It was expectation bias. In the future, I willâŠread all of the incoming CPDLC message, ask for confirmation from the other pilot, and use the âload new routeâ function, and then reverify the clearance from the CPDLC against the FMC before executing the new route in the FMC, using the pilot monitoring to verify that the new clearance loaded correctly.
Multi-Tasking Hazards
â In our descent to Chicago Midway (MDW), we were handed off to a new ATC frequency via CPDLC. We acknowledged and checked in. Center then sent us three CPDLC messages in less than two minutes. We received and acknowledged the first message to descend and maintain FL210. We heard the chime again and saw, âCross MEGGZ at 11,000 feet.â I verified MEGGZ at 11,000 feet in the FMC and on the Mode Control Panel and thought that I acknowledged the CPDLC. We did not see the clearance to proceed direct MEGGZ, which was sent also, but in a separate message. We also had the ACARS chime in the midst of this for landing data, as we were late to accomplish the Descent Checklist. As we were descending through FL200, ATC inquired if we had received the direct MEGGZ and the cross MEGGZ at 11,000 feet messages, because ATC was not showing an acknowledgment from us. We responded that we had received the crossing MEGGZ at 11,000 feet, but not the direct to MEGGZ. When we reviewed the CPDLC log page, we saw the direct to [MEGGZ] message, which we had not acknowledged, and we saw that we had not actually acknowledged the descent to cross MEGGZ at 11,000 feet, either.
First, with expectation bias, I was not thorough, when I heard the chime and saw the ATC message, to ensure I did not have more than one open ATC message. I also missed verifying on the second page of the notification that I accepted. We should have been finished with receiving landing data prior to this stage of flight.
[1] As for CHIRP, ASRS collects voluntarily submitted aviation safety incident/situation reports from pilots, controllers, and others but on a much larger scale (ASRS currently receives 8-10,000 reports a month) and so, unlike CHIRP, they have limited scope to engage with the organisations concerned with individual reports to gain their perspective. As a result, most raw ASRS material is unverified, and some can be a bit emotive or lack perspective, but their alerts and CALLBACK newsletters provide a curated view on topical issues that offer useful areas for thought. For those seeking more data, the ASRS reports database is a public repository that provides the FAA, NASA and other organizations world-wide with research material in support of the promotion of safe flight.
CHIRP contacted the airline concerned but there was no response to our repeated requests for their perspective on extended use of B737 jump-seats.
With the help of our AAIB Advisory Board member, we were able to find some Boeing data from the original certification specs for the B737. Boeingâs sizing for the 737 observer seats was drafted to consider occupants in the range of heights from 5ft 2â (157.5 cm) to 6ft 3â (190.5 cm) in height. We were not able to locate similar ranges for occupant weight/mass, or for other more specific sizing criteria for individual body measurements. The seat is designed to fit within the physical space available in the flight deck, with the following primary considerations:
Given that certification was some time ago it is unlikely that there are more details than this. Looking at the 2020 Anthropometric data for US adults this would include around 95% of men and around 75% of women. That data is for US adults so there is no exact read across to worldwide populations, but it gives a guideline.
It is for the operator to assess the use of the seat, its suitability for long periods, and what mitigations they might want to put in place. The CAAâs role is to identify if they have raised it as an issue and review what, if any, mitigations they feel are appropriate.