Apparatus

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sensors Mode-S transponder

A399E4

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N331DU · operated by DELTA AIR LINES INC

Hex
A399E4
Octal
50714744
Decimal
10,721,764
Country
US
Tail
N331DU
Type
BCS3
Broadcasting now · callsign DAL853 · 35,000 ft
Flights observed
404
Distinct callsigns
20
Country
US
Last broadcast
Jul 26, 22:10 UTC

Current position

A399E4 is currently broadcasting. Map zoomed to live position.

Country allocation

The ICAO 24-bit address A399E4 falls within the block assigned to United States (US) by ICAO Annex 10, Volume III. Every aircraft registered in United States receives a permanent address from this block at the time of registration; the address stays with the airframe even if the aircraft is re-registered to a different operator within the country.

Callsign history 20 distinct

Callsign Airline Flights Last seen
DAL675 Delta Air Lines 11 2026-07-20
DAL2677 Delta Air Lines 11 2026-07-20
DAL541 Delta Air Lines 8 2026-04-18
DAL2565 Delta Air Lines 8 2026-06-19
DAL2985 Delta Air Lines 7 2026-06-05
DAL2958 - 7 2026-06-22
DAL1567 - 7 2026-06-21
DAL1297 Delta Air Lines 7 2026-07-19
DAL816 - 6 2026-07-11
DAL2785 Delta Air Lines 5 2026-07-26
DAL2572 Delta Air Lines 5 2026-04-17
DAL2508 Delta Air Lines 5 2026-04-23
DAL2411 Delta Air Lines 5 2026-06-17
DAL2310 - 5 2026-06-26
DAL2194 Delta Air Lines 5 2026-07-22
DAL1071 Delta Air Lines 5 2026-06-05
DAL928 - 4 2026-07-14
DAL750 Delta Air Lines 4 2026-04-21
DAL303 - 4 2026-07-17
DAL2943 Delta Air Lines 4 2026-06-23

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-26 DAL2785 DTW → STL Jul 26, 19:55 UTCJul 26, 21:50 UTC1h 55m
2026-07-26 DAL2785 DTW → STL Jul 26, 16:25 UTCJul 26, 18:25 UTC2h 0m
2026-07-26 DAL2509 DTW → MSY Jul 26, 13:00 UTCJul 26, 15:15 UTC2h 15m
2026-07-26 DAL2509 DTW → MSY Jul 26, 12:59 UTCJul 26, 15:04 UTC2h 5m
2026-07-25 DAL2586 XNA → ATL Jul 25, 23:05 UTCJul 26, 01:20 UTC2h 15m
2026-07-25 DAL2785 DTW → STL Jul 25, 19:30 UTCJul 25, 21:15 UTC1h 45m
2026-07-25 DAL2785 DTW → STL Jul 25, 16:10 UTCJul 25, 18:15 UTC2h 5m
2026-07-25 DAL2509 DTW → MSY Jul 25, 12:35 UTCJul 25, 14:35 UTC2h 0m
2026-07-25 DAL2586 XNA → ATL Jul 25, 01:35 UTCJul 25, 04:00 UTC2h 25m
2026-07-25 DAL2586 XNA → ATL Jul 25, 01:32 UTCJul 25, 03:55 UTC2h 23m
2026-07-24 DAL1156 BNA → BOS Jul 24, 19:50 UTCJul 24, 23:20 UTC3h 30m
2026-07-24 DAL739 MIA → LAX Jul 24, 14:20 UTCJul 24, 18:00 UTC3h 40m
2026-07-24 DAL2408 MSP → MCI Jul 24, 09:40 UTCJul 24, 12:43 UTC3h 3m
2026-07-24 DAL2408 MSP → MCI Jul 24, 09:45 UTCJul 24, 11:00 UTC1h 15m
2026-07-24 DAL2186 SLC → PHL Jul 24, 04:50 UTCJul 24, 08:15 UTC3h 25m
2026-07-24 DAL2186 SLC → PHL Jul 24, 04:49 UTCJul 24, 08:06 UTC3h 17m
2026-07-23 DAL831 SEA → AUS Jul 23, 23:40 UTCJul 24, 03:35 UTC3h 55m
2026-07-23 DAL831 SEA → AUS Jul 23, 18:25 UTCJul 23, 22:05 UTC3h 40m
2026-07-23 DAL372 BNA → SEA Jul 23, 12:25 UTCJul 23, 16:50 UTC4h 25m
2026-07-23 DAL815 LAS → BOS Jul 23, 04:35 UTCJul 23, 08:25 UTC3h 50m
2026-07-22 DAL373 PDX → ATL Jul 22, 22:15 UTCJul 23, 02:40 UTC4h 25m
2026-07-22 DAL2748 MSP → FSD Jul 22, 18:25 UTCJul 22, 20:20 UTC1h 55m
2026-07-22 DAL2194 BDL → ATL Jul 22, 15:35 UTCJul 22, 16:50 UTC1h 15m
2026-07-22 DAL2194 BDL → ATL Jul 22, 12:30 UTCJul 22, 14:10 UTC1h 40m
2026-07-21 DAL2767 CMH → ATL Jul 21, 11:15 UTCJul 21, 13:20 UTC2h 5m
2026-07-21 DAL2804 ATL → DAY Jul 21, 03:05 UTCJul 21, 05:20 UTC2h 15m
2026-07-20 DAL2677 MSP → MCO Jul 20, 23:10 UTCJul 21, 01:25 UTC2h 15m
2026-07-20 DAL2677 MSP → MCO Jul 20, 19:20 UTCJul 20, 21:30 UTC2h 10m
2026-07-20 DAL675 BOS → FLL Jul 20, 15:10 UTCJul 20, 17:45 UTC2h 35m
2026-07-19 DAL1297 LGA → MSY Jul 19, 20:25 UTCJul 19, 23:10 UTC2h 45m
2026-07-18 DAL1297 LGA → MSY Jul 18, 18:55 UTCJul 18, 21:25 UTC2h 30m
2026-07-18 DAL675 BOS → MCI Jul 18, 13:31 UTCJul 18, 16:26 UTC2h 55m
2026-07-18 DAL675 - Jul 18, 13:35 UTCJul 18, 16:30 UTC2h 55m
2026-07-17 DAL462 DFW → BOS Jul 17, 23:00 UTCJul 18, 02:19 UTC3h 20m
2026-07-17 DAL303 BOS → DFW Jul 17, 16:19 UTCJul 17, 19:45 UTC3h 25m
2026-07-17 DAL2828 ORD → BOS Jul 17, 13:00 UTCJul 17, 14:55 UTC1h 55m
2026-07-17 DAL2804 BOS → ORD Jul 17, 01:45 UTCJul 17, 03:59 UTC2h 15m
2026-07-16 DAL1156 - Jul 16, 19:55 UTCJul 17, 00:04 UTC4h 10m
2026-07-16 DAL739 SEA → AUS Jul 16, 14:50 UTCJul 16, 18:40 UTC3h 50m
2026-07-16 DAL925 - Jul 16, 09:40 UTCJul 16, 12:30 UTC2h 50m
2026-07-16 DAL936 SEA → ANC Jul 16, 04:40 UTCJul 16, 07:55 UTC3h 15m
2026-07-15 DAL373 BNA → SEA Jul 15, 22:25 UTCJul 16, 02:45 UTC4h 20m
2026-07-15 DAL1710 SEA → BNA Jul 15, 16:50 UTCJul 15, 21:00 UTC4h 10m
2026-07-15 DAL1731 DEN → SEA Jul 15, 12:45 UTCJul 15, 14:55 UTC2h 10m
2026-07-15 DAL2851 SEA → DEN Jul 15, 03:25 UTCJul 15, 05:40 UTC2h 15m
2026-07-14 DAL2449 PHX → SEA Jul 14, 23:05 UTCJul 15, 01:30 UTC2h 25m
2026-07-14 DAL2449 SEA → PHX Jul 14, 19:10 UTCJul 14, 21:50 UTC2h 40m
2026-07-14 DAL853 ANC → SEA Jul 14, 14:06 UTCJul 14, 17:03 UTC2h 57m
2026-07-14 DAL928 - Jul 14, 14:10 UTCJul 14, 17:00 UTC2h 50m
2026-07-13 DAL928 SEA → ANC Jul 13, 21:48 UTCJul 14, 01:18 UTC3h 30m

About Mode-S

A Mode-S transponder code (also called an "ICAO 24-bit address" or "hex code") is a 6-character hexadecimal identifier permanently assigned to an aircraft when it's first registered. Unlike callsigns (which change with each flight) or registrations (which can change if an aircraft is sold internationally), the Mode-S address stays with the airframe for the life of the aircraft in that country.

Every ADS-B transmission from an aircraft includes its Mode-S address, making it the most reliable way to identify a specific airframe. Flight-tracking services like Apparatus use the Mode-S address as the primary key for tying position broadcasts, callsigns, and ownership records together.

Prefer a tail-number view? See the N331DU page for operator, model, and routing details .

Mode-S A399E4 frequently asked

What is Mode-S code A399E4?
A399E4 is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N331DU.
Where is Mode-S A399E4 registered?
Mode-S code A399E4 is allocated to United States (US). All aircraft registered there receive a Mode-S address from a fixed block defined by ICAO Annex 10.
Is A399E4 broadcasting right now?
Yes. Mode-S A399E4 is currently airborne.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex A399E4, octal 50714744, decimal 10,721,764.
What flights does A399E4 operate?
Mode-S A399E4 has broadcast 20 distinct callsigns, including DAL675, DAL2677, DAL541, DAL2565, DAL2985.