Date: 201909
Local time of day: 1201-1800
Location: IAH.Airport, TX
Flight conditions: Marginal
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class B IAH
ATC / advisory: Tower IAH
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Workload; Time Pressure; Human-Machine Interface
Second reporter function: First Officer; Pilot Flying
Anomaly: ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Provided Assistance
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: We received our clearance through the Air Traffic Control Data Link system on the CDU (Control Display Unit). The clearance was reviewed by both the FO (First Officer) & CA (Captain); which read cleared BLTWY 6. Both the FO and CA reviewed the SID and confirmed the TOP ALTITUDE 16;000. Given our takeoff clearance; we were told to turn left 360 degrees. After TO (Takeoff); there was radio congestion on the frequency preventing the tower from transferring us to departure control. After a lengthy time; I inquired to change to departure control. Upon checking in with IAH Departure; I called 'Aircraft X climbing to 16;000 on a heading of 360.' Departure replied; 'Roger; maintain 16;000.' After a few moments; ATC asked us what altitude Tower had given us on departure. I replied; 16;000. ATC then advised us of a possible altitude deviation and to standby for a phone number. I replied that we were given the BLTWY 6 RNAV Dep with an altitude of 16;000. ATC then gave me a phone number to call. After arrival; I called IAH Tower as requested. In that conversation; the Tower manager said that we were given 4;000 feet per the CPDLC over ACARS. This is the first time that we were informed on the 4;000 restriction. I explained that neither the FO nor I saw that altitude clearance and we understood 16;000 was our clearance. A conversation ensued about the fact that we did not receive the CPDLC over ACARS and received the clearance via the Air Traffic Control Data Link system which does not allow printing of the clearance.Receiving the ATC clearance over the Air Traffic Control Data Link system without the ability to print the clearance and crosscheck with the FMS (Flight Management System) & SID is cumbersome. The clearance is displayed on a small screen; often times with multiple pages for the clearance. When reviewing the clearance; and paging through each page can cause the pilot to miss the full clearance. In this case; we both separately reviewed the clearance on the CDU and did not see the altitude restriction of 4;000. When given our takeoff clearance; we were given a heading of 360 and no altitude assignment. Give the ability to print and view the entire clearance as a whole. We review the Flight plan; Closeout; ATIS all as a whole document on our iPad or on paper. None of those do you have to page through to see the entire clearance. In addition; with the ability to print the clearance - pilots would have the ability to review throughout the preflight and taxi timeframe without accessing the Air Traffic Control Data Link system pages on the CDU. I suggest when an altitude is different from the TOP ALTITUDE on the SID that ATC give that altitude in their takeoff clearance - since this is different from the published altitude on the SID. This would provide another layer of safety just like on a RNAV departure - ATC gives the cleared to first fix in their takeoff clearance.


Second narrative: We received our clearance via CPDLC. We both looked at clearance. I was the pilot flying. On the departure it says an altitude of 16;000. We took off and were climbing to 16;000. There was a delay when switching to departure because the tower controller was busy. When we checked in with departure he said to climb to 16;000. He then asked what altitude we were cleared to and the captain said 16;000. He then told us of a possible ATC deviation and gave us a phone number to call. After landing the Captain called and he said that they said we were only cleared to 4;000 via the CPDLC. Neither one of us saw 4;000 and since we left the airplane on our way to the next fly we couldn't check the CPCLC lot. By not being able to print the CPDLC clearance to review.CPDLC needs to be able to be printed. Especially important after a route change. I feel that if there is any deviation in the route such as an altitude different then on SID or different route points than filed it should be required to have a printed copy via PDC or by voice from clearance.


Synopsis: Air Carrier flight crew reported missed altitude restriction in clearance.